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Sunscreen, also known as sunblock or sun cream, is a
photoprotective Photoprotection is the biochemical process that helps organisms cope with molecular damage caused by sunlight. Plants and other oxygenic phototrophs have developed a suite of photoprotective mechanisms to prevent photoinhibition and oxidative st ...
topical A topical medication is a medication that is applied to a particular place on or in the body. Most often topical medication means application to body surfaces such as the skin or mucous membranes to treat ailments via a large range of classes ...
product for the
skin Skin is the layer of usually soft, flexible outer tissue covering the body of a vertebrate animal, with three main functions: protection, regulation, and sensation. Other cuticle, animal coverings, such as the arthropod exoskeleton, have diffe ...
that mainly absorbs, or to a much lesser extent reflects, some of the
sun The Sun is the star at the center of the Solar System. It is a nearly perfect ball of hot plasma, heated to incandescence by nuclear fusion reactions in its core. The Sun radiates this energy mainly as light, ultraviolet, and infrared radi ...
's
ultraviolet Ultraviolet (UV) is a form of electromagnetic radiation with wavelength from 10 nanometer, nm (with a corresponding frequency around 30 Hertz, PHz) to 400 nm (750 Hertz, THz), shorter than that of visible light, but longer than ...
(UV) radiation and thus helps protect against
sunburn Sunburn is a form of radiation burn that affects living tissue, such as skin, that results from an overexposure to ultraviolet (UV) radiation, usually from the Sun. Common symptoms in humans and animals include: red or reddish skin that is ho ...
and most importantly prevent
skin cancer Skin cancers are cancers that arise from the skin. They are due to the development of abnormal cells that have the ability to invade or spread to other parts of the body. There are three main types of skin cancers: basal-cell skin cancer (BCC) ...
. Sunscreens come as
lotion Lotion is a low-viscosity topical preparation intended for application to the skin. By contrast, creams and gels have higher viscosity, typically due to lower water content. Lotions are applied to external skin with bare hands, a brush, a clean ...
s, sprays, gels, foams (such as an expanded foam lotion or whipped lotion), sticks, powders and other topical products. Sunscreens are common supplements to clothing, particularly
sunglasses Sunglasses or sun glasses (informally called shades or sunnies; more names below) are a form of protective eyewear designed primarily to prevent bright sunlight and high-energy visible light from damaging or discomforting the eyes. They can s ...
, sunhats and special
sun protective clothing Sun protective clothing is clothing specifically designed for sun protection and is produced from a fabric rated for its level of ultraviolet (UV) protection. A novel weave structure and denier (related to thread count per inch) may produce sun p ...
, and other forms of photoprotection (such as
umbrella An umbrella or parasol is a folding canopy supported by wooden or metal ribs that is usually mounted on a wooden, metal, or plastic pole. It is designed to protect a person against rain or sunlight. The term ''umbrella'' is traditionally used ...
s). The first sunscreen in the world was invented in Australia, by chemist H.A. Milton Blake, in 1932 formulating with the UV filter 'salol' (
phenyl salicylate Phenyl salicylate, or salol, is the organic compound with the formula C6H5O2C6H4OH. It is a white solid. It is occasionally used in sunscreens and as an antiseptic. Production and reactions The title compound was synthesized first in 1883 by th ...
) at a concentration of 10%. Its protection was verified by the University of Adelaide and it was also produced commercially by Blake's company, Hamilton Laboratories. Despite sunscreen being relatively new, sun protection practices have been observed since at least the ancient Egyptians "who used ingredients such as rice bran, jasmine, and lupine" to provide sun protection. Sunscreens are classified into mineral (also referred to as physical) sunscreens (i.e.,
zinc oxide Zinc oxide is an inorganic compound with the formula . It is a white powder that is insoluble in water. ZnO is used as an additive in numerous materials and products including cosmetics, food supplements, rubbers, plastics, ceramics, glass, cemen ...
and
titanium dioxide Titanium dioxide, also known as titanium(IV) oxide or titania , is the inorganic compound with the chemical formula . When used as a pigment, it is called titanium white, Pigment White 6 (PW6), or CI 77891. It is a white solid that is insolubl ...
) and chemical (also referred to as petrochemical, as they are typically derived from petroleum) sunscreens. Research by the FDA on the safety of the main three organic UV filters (
oxybenzone Oxybenzone or benzophenone-3 or BP-3 (trade names Milestab 9, Eusolex 4360, Escalol 567, KAHSCREEN BZ-3) is an organic compound. It is a pale-yellow solid that is readily soluble in most organic solvents. Oxybenzone belongs to the class of aroma ...
,
homosalate Homosalate is an organic compound used in some sunscreens. It is made by the Fischer–Speier esterification of salicylic acid and 3,3,5-trimethylcyclohexanol, the latter being a hydrogenated derivative of isophorone. Contained in 45% of U.S. su ...
and
octocrylene Octocrylene is an organic compound used as an ingredient in sunscreens and cosmetics. It is an ester formed by the condensation of 2-ethylhexyl cyanoacetate with benzophenone. It is a viscous, oily liquid that is clear and colorless. The exten ...
) found that the three ingredients could be detected on the skin, in blood, in breast milk and in urine samples weeks after no longer being used. Medical organizations such as the
American Cancer Society The American Cancer Society (ACS) is a nationwide voluntary health organization dedicated to eliminating cancer. Established in 1913, the society is organized into six geographical regions of both medical and lay volunteers operating in more than ...
recommend the use of sunscreen because it aids in the prevention of squamous cell carcinomas. The routine use of sunscreens may also reduce the risk of
melanoma Melanoma, also redundantly known as malignant melanoma, is a type of skin cancer that develops from the pigment-producing cells known as melanocytes. Melanomas typically occur in the skin, but may rarely occur in the mouth, intestines, or eye ( ...
. However, many sunscreens do not block
ultraviolet A Ultraviolet (UV) is a form of electromagnetic radiation with wavelength from 10 nm (with a corresponding frequency around 30  PHz) to 400 nm (750  THz), shorter than that of visible light, but longer than X-rays. UV radiation i ...
(UVA) radiation, yet protection from UVA is important for the prevention of skin cancer. To provide a better indication of their ability to protect against skin cancer and other diseases associated with UVA radiation (such as
phytophotodermatitis Phytophotodermatitis, also known as berloque dermatitis or margarita photodermatitis, is a cutaneous phototoxic inflammatory reaction resulting from contact with a light-sensitizing botanical agent followed by exposure to ultraviolet light (from t ...
), the use of broad-spectrum ( UVA/UVB) sunscreens has been recommended. In the United States, sunscreens are required to remain effective at original strength for at least three years. Some sunscreens include an
expiration date An expiration date or expiry date is a previously determined date after which something should no longer be used, either by operation of law or by exceeding the anticipated shelf life for perishable goods. Expiration dates are applied to selecte ...
—a date indicating when they may become less effective.


Health effects


Benefits

Sunscreen use can help prevent
melanoma Melanoma, also redundantly known as malignant melanoma, is a type of skin cancer that develops from the pigment-producing cells known as melanocytes. Melanomas typically occur in the skin, but may rarely occur in the mouth, intestines, or eye ( ...
and
squamous cell carcinoma Squamous-cell carcinomas (SCCs), also known as epidermoid carcinomas, comprise a number of different types of cancer that begin in squamous cells. These cells form on the surface of the skin, on the lining of hollow organs in the body, and on the ...
, two types of
skin cancer Skin cancers are cancers that arise from the skin. They are due to the development of abnormal cells that have the ability to invade or spread to other parts of the body. There are three main types of skin cancers: basal-cell skin cancer (BCC) ...
. There is little evidence that it is effective in preventing
basal cell carcinoma Basal-cell carcinoma (BCC), also known as basal-cell cancer, is the most common type of skin cancer. It often appears as a painless raised area of skin, which may be shiny with small blood vessels running over it. It may also present as a raise ...
. A 2013 study concluded that the diligent, everyday application of sunscreen could slow or temporarily prevent the development of wrinkles and sagging skin. The study involved 900
white White is the lightest color and is achromatic (having no hue). It is the color of objects such as snow, chalk, and milk, and is the opposite of black. White objects fully reflect and scatter all the visible wavelengths of light. White on ...
people in Australia and required some of them to apply a broad-spectrum sunscreen every day for four and a half years. It found that people who did so had noticeably more resilient and smoother skin than those assigned to continue their usual practices. A study on 32 subjects showed that daily use of sunscreen (SPF 30) reversed
photoaging Photoaging or photoageing (also known as "dermatoheliosis") is a term used for the characteristic changes to skin induced by chronic UVA and UVB exposure. Tretinoin is the best studied retinoid in the treatment of photoaging. The deterioration ...
of the skin within 12 weeks and the amelioration continued until the end of the investigation period of one year. Sunscreen is inherently anti-ageing as the sun is the number one cause of premature ageing, it therefore may slow or temporarily prevent the development of wrinkles, dark spots and sagging skin. Minimizing UV damage is especially important for children and fair-skinned individuals and those who have sun sensitivity for medical reasons.


Risks

As of 2021, only Zinc Oxide and Titanium Dioxide are recognised as safe and effective (GRASE) by the U.S. Food and Drug Administration (FDA), as currently there is insufficient safety data to support petrochemicals being safe, such as oxybenzone and avobenzone. "A survey of 1000 Australians from 18 to over 76 years old, commissioned by Cancer Council, found that nearly half of respondents believed that sunscreen contained chemicals that were bad for you and could even cause cancer." In 2009, the
Therapeutic Goods Administration The Therapeutic Goods Administration (TGA) is the medicine and therapeutic regulatory agency of the Australian Government. As part of the Department of Health and Aged Care, the TGA regulates the quality, supply and advertising of medicines, pa ...
of Australia updated a review of sunscreen safety studies and concluded: "The potential for titanium dioxide (TiO2) and zinc oxide (ZnO) nanoparticles in sunscreens to cause adverse effects depend primarily upon the ability of the nanoparticles to reach viable skin cells. To date, the current weight of evidence suggests that TiO2 and ZnO nanoparticles do not reach viable skin cells." Many petrochemical based sunscreen ingredients have already been banned over safety concerns (petrochemicals such as PABA). There is a risk of an allergic reaction to sunscreen for some individuals, as "Typical allergic contact dermatitis may occur in individuals allergic to any of the ingredients that are found in sunscreen products or cosmetic preparations that have a sunscreen component. The rash can occur anywhere on the body where the substance has been applied and sometimes may spread to unexpected sites."


Vitamin D production

There are some concerns about potential
vitamin D deficiency Vitamin D deficiency or hypovitaminosis D is a vitamin D level that is below normal. It most commonly occurs in people when they have inadequate exposure to sunlight, particularly sunlight with adequate ultraviolet B rays (UVB). Vitamin D defic ...
arising from prolonged use of sunscreen. The typical use of sunscreen does not usually result in vitamin D deficiency; however, extensive usage may. Sunscreen prevents ultraviolet light from reaching the skin, and even moderate protection can substantially reduce vitamin D synthesis. However, adequate amounts of vitamin D can obtained via diet or supplements. Vitamin D overdose is impossible from UV exposure due to an equilibrium the skin reaches in which vitamin D degrades as quickly as it is created. Studies showed that sunscreen with a high UVA protection factor enabled significantly higher vitamin D synthesis than a low UVA protection factor sunscreen, likely because it allows more UVB transmission.


Measurements of protection


Sun protection factor and labeling

The sun protection factor (SPF rating, introduced in 1974) is a measure of the fraction of sunburn-producing UV rays that reach the skin. For example, "SPF 15" means that of the burning radiation will reach the skin, assuming sunscreen is applied evenly at a thick dosage of 2 milligrams per square centimeter (mg/cm2). It is important to note that sunscreens with higher SPF do not last or remain effective on the skin any longer than lower SPF and must be continually reapplied as directed, usually every two hours. The SPF is an imperfect measure of skin damage because invisible damage and skin malignant melanomas are also caused by
ultraviolet A Ultraviolet (UV) is a form of electromagnetic radiation with wavelength from 10 nm (with a corresponding frequency around 30  PHz) to 400 nm (750  THz), shorter than that of visible light, but longer than X-rays. UV radiation i ...
(UVA, wavelengths 315–400 or 320–400 nm), which does not primarily cause reddening or pain. Conventional sunscreen blocks very little UVA radiation relative to the nominal SPF; broad-spectrum sunscreens are designed to protect against both UVB and UVA. According to a 2004 study, UVA also causes
DNA damage DNA repair is a collection of processes by which a cell identifies and corrects damage to the DNA molecules that encode its genome. In human cells, both normal metabolic activities and environmental factors such as radiation can cause DNA da ...
to cells deep within the skin, increasing the risk of
malignant melanoma Melanoma, also redundantly known as malignant melanoma, is a type of skin cancer that develops from the Biological pigment, pigment-producing cells known as melanocytes. Melanomas typically occur in the skin, but may rarely occur in the mouth, i ...
s. Even some products labeled "broad-spectrum UVA/UVB protection" have not always provided good protection against UVA rays.
Titanium dioxide Titanium dioxide, also known as titanium(IV) oxide or titania , is the inorganic compound with the chemical formula . When used as a pigment, it is called titanium white, Pigment White 6 (PW6), or CI 77891. It is a white solid that is insolubl ...
probably gives good protection, but does not completely cover the UVA spectrum, as early 2000s research suggests that zinc oxide is superior to titanium dioxide at wavelengths 340–380 nm. Owing to consumer confusion over the real degree and duration of protection offered, labeling restrictions are enforced in several countries. In the EU, sunscreen labels can only go up to SPF 50+ (initially listed as 30 but soon revised to 50).
Australia Australia, officially the Commonwealth of Australia, is a Sovereign state, sovereign country comprising the mainland of the Australia (continent), Australian continent, the island of Tasmania, and numerous List of islands of Australia, sma ...
's
Therapeutic Goods Administration The Therapeutic Goods Administration (TGA) is the medicine and therapeutic regulatory agency of the Australian Government. As part of the Department of Health and Aged Care, the TGA regulates the quality, supply and advertising of medicines, pa ...
increased the upper limit to 50+ in 2012. In its 2007 and 2011 draft rules, the US
Food and Drug Administration The United States Food and Drug Administration (FDA or US FDA) is a List of United States federal agencies, federal agency of the United States Department of Health and Human Services, Department of Health and Human Services. The FDA is respon ...
(FDA) proposed a maximum SPF label of 50, to limit unrealistic claims. (As of February 2017, the FDA has not adopted the SPF 50 limit.) Others have proposed restricting the active ingredients to an SPF of no more than 50, due to lack of evidence that higher dosages provide more meaningful protection. Different sunscreen ingredients have different effectiveness against UVA and UVB. The SPF can be measured by applying sunscreen to the skin of a volunteer and measuring how long it takes before sunburn occurs when exposed to an artificial sunlight source. In the US, such an ''
in vivo Studies that are ''in vivo'' (Latin for "within the living"; often not italicized in English) are those in which the effects of various biological entities are tested on whole, living organisms or cells, usually animals, including humans, and ...
'' test is required by the FDA. It can also be measured ''
in vitro ''In vitro'' (meaning in glass, or ''in the glass'') studies are performed with microorganisms, cells, or biological molecules outside their normal biological context. Colloquially called "test-tube experiments", these studies in biology an ...
'' with the help of a specially designed
spectrometer A spectrometer () is a scientific instrument used to separate and measure spectral components of a physical phenomenon. Spectrometer is a broad term often used to describe instruments that measure a continuous variable of a phenomenon where the ...
. In this case, the actual
transmittance Transmittance of the surface of a material is its effectiveness in transmitting radiant energy. It is the fraction of incident electromagnetic power that is transmitted through a sample, in contrast to the transmission coefficient, which is th ...
of the sunscreen is measured, along with the degradation of the product due to being exposed to sunlight. In this case, the transmittance of the sunscreen must be measured over all wavelengths in sunlight's UVB–UVA range (290–400 nm), along with a table of how effective various wavelengths are in causing sunburn (the ''erythemal action spectrum'') and the standard intensity
spectrum A spectrum (plural ''spectra'' or ''spectrums'') is a condition that is not limited to a specific set of values but can vary, without gaps, across a continuum. The word was first used scientifically in optics to describe the rainbow of colors i ...
of sunlight (see the figure). Such ''in vitro'' measurements agree very well with ''in vivo'' measurements. Numerous methods have been devised for evaluation of UVA and UVB protection. The most-reliable spectrophotochemical methods eliminate the subjective nature of grading
erythema Erythema (from the Greek , meaning red) is redness of the skin or mucous membranes, caused by hyperemia (increased blood flow) in superficial capillaries. It occurs with any skin injury, infection, or inflammation. Examples of erythema not assoc ...
. The ultraviolet protection factor (UPF) is a similar scale developed for rating fabrics for
sun protective clothing Sun protective clothing is clothing specifically designed for sun protection and is produced from a fabric rated for its level of ultraviolet (UV) protection. A novel weave structure and denier (related to thread count per inch) may produce sun p ...
. According to recent testing by ''
Consumer Reports Consumer Reports (CR), formerly Consumers Union (CU), is an American nonprofit consumer organization dedicated to independent product testing, investigative journalism, consumer-oriented research, public education, and consumer advocacy. Founded ...
'', UPF ~30+ is typical for protective fabrics, while UPF ~20 is typical for standard summer fabrics. Mathematically, the SPF (or the UPF) is calculated from measured data as: \mathrm = \frac, where E(\lambda) is the solar irradiance spectrum, A(\lambda) the erythemal action spectrum, and \mathrm(\lambda) the monochromatic protection factor, all functions of the wavelength \lambda. The MPF is roughly the inverse of the transmittance at a given wavelength. The above means that the SPF is not simply the inverse of the transmittance in the UVB region. If that were true, then applying two layers of SPF 5 sunscreen would always be equivalent to SPF 25 (5 times 5). The actual combined SPF may be lower than the square of the single-layer SPF.


UVA protection


Persistent pigment darkening

The persistent pigment darkening (PPD) method is a method of measuring UVA protection, similar to the SPF method of measuring sunburn protection. Originally developed in Japan, it is the preferred method used by manufacturers such as
L'Oréal L'Oréal S.A. () is a French personal care company headquartered in Clichy, Hauts-de-Seine with a registered office in Paris. It is the world's largest cosmetics company and has developed activities in the field concentrating on hair color, sk ...
. Instead of measuring
erythema Erythema (from the Greek , meaning red) is redness of the skin or mucous membranes, caused by hyperemia (increased blood flow) in superficial capillaries. It occurs with any skin injury, infection, or inflammation. Examples of erythema not assoc ...
, the PPD method uses UVA radiation to cause a persistent darkening or tanning of the skin. Theoretically, a sunscreen with a PPD rating of 10 should allow a person 10 times as much UVA exposure as would be without protection. The PPD method is an ''
in vivo Studies that are ''in vivo'' (Latin for "within the living"; often not italicized in English) are those in which the effects of various biological entities are tested on whole, living organisms or cells, usually animals, including humans, and ...
'' test like SPF. In addition, the European Cosmetic and Perfumery Association (''Colipa'') has introduced a method that, it is claimed, can measure this ''
in vitro ''In vitro'' (meaning in glass, or ''in the glass'') studies are performed with microorganisms, cells, or biological molecules outside their normal biological context. Colloquially called "test-tube experiments", these studies in biology an ...
'' and provide parity with the PPD method.


SPF equivalence

As part of revised guidelines for sunscreens in the EU, there is a requirement to provide the consumer with a minimum level of UVA protection in relation to the SPF. This should be a UVA protection factor of at least 1/3 of the SPF to carry the UVA seal. The 1/3 threshold derives from the European Commission recommendation 2006/647/EC. This Commission recommendation specifies that the UVA protection factor should be measured using the PPD method as modified by the French health agency AFSSAPS (now ANSM) "or an equivalent degree of protection obtained with any in vitro method". A set of final US FDA rules effective from summer 2012 defines the phrase "broad spectrum" as providing UVA protection proportional to the UVB protection, using a standardized testing method.


Star rating system

In the UK and Ireland, the
Boots A boot is a type of footwear. Boot or Boots may also refer to: Businesses * Boot Inn, Chester, Cheshire, England * Boots (company), a high-street pharmacy chain and manufacturer of pharmaceuticals in the United Kingdom * The Boot, Cromer Stre ...
star rating system is a proprietary ''
in vitro ''In vitro'' (meaning in glass, or ''in the glass'') studies are performed with microorganisms, cells, or biological molecules outside their normal biological context. Colloquially called "test-tube experiments", these studies in biology an ...
'' method used to describe the ratio of UVA to UVB protection offered by sunscreen creams and sprays. Based on original work by Brian Diffey at
Newcastle University Newcastle University (legally the University of Newcastle upon Tyne) is a UK public university, public research university based in Newcastle upon Tyne, North East England. It has overseas campuses in Singapore and Malaysia. The university is ...
, the Boots Company in Nottingham, UK, developed a method that has been widely adopted by companies marketing these products in the UK. One-star products provide the lowest ratio of UVA protection, five-star products the highest. The method was revised in light of the Colipa UVA PF test and the revised EU recommendations regarding UVA PF. The method still uses a spectrophotometer to measure absorption of UVA versus UVB; the difference stems from a requirement to pre-irradiate samples (where this was not previously required) to give a better indication of UVA protection and photostability when the product is used. With the current methodology, the lowest rating is three stars, the highest being five stars. In August 2007, the FDA put out for consultation the proposal that a version of this protocol be used to inform users of American product of the protection that it gives against UVA; but this was not adopted, for fear it would be too confusing.


PA system

Asian brands, particularly Japanese ones, tend to use The Protection Grade of UVA (PA) system to measure the UVA protection that a sunscreen provides. The PA system is based on the PPD reaction and is now widely adopted on the labels of sunscreens. According to the Japan Cosmetic Industry Association, PA+ corresponds to a UVA protection factor between two and four, PA++ between four and eight, and PA+++ more than eight. This system was revised in 2013 to include PA++++ which corresponds to a PPD rating of sixteen or above.


Sunblock

Sunblock typically refers to opaque sunscreen that is effective at blocking both UVA and UVB rays and uses a heavy carrier oil to resist being washed off.
Titanium dioxide Titanium dioxide, also known as titanium(IV) oxide or titania , is the inorganic compound with the chemical formula . When used as a pigment, it is called titanium white, Pigment White 6 (PW6), or CI 77891. It is a white solid that is insolubl ...
and
zinc oxide Zinc oxide is an inorganic compound with the formula . It is a white powder that is insoluble in water. ZnO is used as an additive in numerous materials and products including cosmetics, food supplements, rubbers, plastics, ceramics, glass, cemen ...
are two minerals that are used in sunblock. The use of the word "sunblock" in the marketing of sunscreens is controversial. Since 2013, the FDA has banned such use because it can lead consumers to overestimate the effectiveness of products so labeled. Nonetheless, many consumers use the words sunblock and sunscreen synonymously. For total protection against damage from the sun, the skin needs to be protected from UVA, UVB, and also IRA (
infrared Infrared (IR), sometimes called infrared light, is electromagnetic radiation (EMR) with wavelengths longer than those of visible light. It is therefore invisible to the human eye. IR is generally understood to encompass wavelengths from around ...
-A light). Infrared radiation accounts for roughly 40% of solar energy at sea level. There is continuing debate within the dermatology community over the impact of sun-sourced IRA: Some sources indicate that early morning IRA exposure may be protective against further sun exposure by increasing cell proliferation and initiating anti-inflammatory cascades; these effects are not observed for artificial sources of intense IRA.


Active ingredients

In addition to
moisturizer A moisturizer, or emollient, is a cosmetic preparation used for protecting, moisturizing, and lubricating the skin. These functions are normally performed by sebum produced by healthy skin. The word "emollient" is derived from the Latin verb ''mo ...
s and other inactive ingredients, sunscreens contain one or more of the following active ingredients, which are either organic or mineral in nature: *
Organic chemical In chemistry, organic compounds are generally any chemical compounds that contain carbon-hydrogen or carbon-carbon bonds. Due to carbon's ability to catenate (form chains with other carbon atoms), millions of organic compounds are known. The st ...
compounds that absorb ultraviolet light. * Inorganic
particulates Particulates – also known as atmospheric aerosol particles, atmospheric particulate matter, particulate matter (PM) or suspended particulate matter (SPM) – are microscopic particles of solid or liquid matter suspended in the air. The ter ...
that reflect, scatter, and absorb UV light (such as
titanium dioxide Titanium dioxide, also known as titanium(IV) oxide or titania , is the inorganic compound with the chemical formula . When used as a pigment, it is called titanium white, Pigment White 6 (PW6), or CI 77891. It is a white solid that is insolubl ...
,
zinc oxide Zinc oxide is an inorganic compound with the formula . It is a white powder that is insoluble in water. ZnO is used as an additive in numerous materials and products including cosmetics, food supplements, rubbers, plastics, ceramics, glass, cemen ...
, or a combination of both). * Organic particulates that mostly absorb UV light like organic chemical compounds, but contain multiple
chromophores A chromophore is the part of a molecule responsible for its color. The color that is seen by our eyes is the one not absorbed by the reflecting object within a certain wavelength spectrum of visible light. The chromophore is a region in the molec ...
that reflect and scatter a fraction of light like inorganic particulates. An example is Tinosorb M. The mode of action is about 90% by absorption and 10% by scattering. The principal active ingredients in sunscreens are usually
aromatic In chemistry, aromaticity is a chemical property of cyclic ( ring-shaped), ''typically'' planar (flat) molecular structures with pi bonds in resonance (those containing delocalized electrons) that gives increased stability compared to satur ...
molecules conjugated with
carbonyl In organic chemistry, a carbonyl group is a functional group composed of a carbon atom double-bonded to an oxygen atom: C=O. It is common to several classes of organic compounds, as part of many larger functional groups. A compound containing a ...
groups. This general structure allows the molecule to absorb high-energy ultraviolet rays and release the energy as lower-energy rays, thereby preventing the skin-damaging ultraviolet rays from reaching the skin. So, upon exposure to UV light, most of the ingredients (with the notable exception of
avobenzone Avobenzone ( trade names Parsol 1789, Milestab 1789, Eusolex 9020, Escalol 517, Neo Heliopan 357 and others, INCI Butyl Methoxydibenzoylmethane) is an oil-soluble ingredient used in sunscreen products to absorb the full spectrum of UVA rays. Hi ...
) do not undergo significant chemical change, allowing these ingredients to retain the UV-absorbing potency without significant
photodegradation Photodegradation is the alteration of materials by light. Commonly, the term is used loosely to refer to the combined action of sunlight and air, which cause oxidation and hydrolysis. Often photodegradation is intentionally avoided, since it destroy ...
. A chemical stabilizer is included in some sunscreens containing avobenzone to slow its breakdown; examples include formulations containing. The stability of avobenzone can also be improved by
bemotrizinol Bemotrizinol ( INN/USAN, INCI bis-ethylhexyloxyphenol methoxyphenyl triazine) is an oil-soluble organic compound that is added to sunscreens to absorb UV rays. It is marketed as Parsol Shield, Tinosorb S, and Escalol S. Bemotrizinol is a broad-s ...
,
octocrylene Octocrylene is an organic compound used as an ingredient in sunscreens and cosmetics. It is an ester formed by the condensation of 2-ethylhexyl cyanoacetate with benzophenone. It is a viscous, oily liquid that is clear and colorless. The exten ...
and various other photostabilisers. Most organic compounds in sunscreens slowly degrade and become less effective over the course of several years even if stored properly, resulting in the expiration dates calculated for the product. Sunscreening agents are used in some hair care products such as shampoos, conditioners and styling agents to protect against protein degradation and color loss. Currently,
benzophenone-4 Sulisobenzone (benzophenone-4) is an ingredient in some sunscreens which protects the skin from damage by UVB and UVA ultraviolet light. Its sodium salt, sulisobenzone sodium, is also referred to as benzophenone-5. References

Benzenesulf ...
and ethylhexyl methoxycinnamate are the two sunscreens most commonly used in hair products. The common sunscreens used on skin are rarely used for hair products due to their texture and weight effects. The following are the FDA allowable active ingredients in sunscreens: Zinc oxide was approved as a UV filter by the EU in 2016. Other ingredients approved within the EU and other parts of the world, that have not been included in the current FDA Monograph: * Time and Extent Application (TEA), Proposed Rule on FDA approval originally expected 2009, now expected 2015. Many of the ingredients awaiting approval by the FDA are relatively new, and developed to absorb UVA. The 2014 Sunscreen Innovation Act was passed to accelerate the FDA approval process.


Inactive ingredients

It is known that SPF is affected by not only the choice of active ingredients and the percentage of active ingredients but also the formulation of the vehicle/base. Final SPF is also impacted by the distribution of active ingredients in the sunscreen, how evenly the sunscreen applies on the skin, how well it dries down on the skin and the pH value of the product among other factors. Changing any inactive ingredient may potentially alter a sunscreen's SPF. When combined with UV filters, added
antioxidant Antioxidants are compounds that inhibit oxidation, a chemical reaction that can produce free radicals. This can lead to polymerization and other chain reactions. They are frequently added to industrial products, such as fuels and lubricant ...
s can work synergistically to affect the overall SPF value positively. Furthermore, adding antioxidants to sunscreen can amplify its ability to reduce markers of extrinsic photoaging, grant better protection from UV induced pigment formation, mitigate skin
lipid peroxidation Lipid peroxidation is the chain of reactions of oxidative degradation of lipids. It is the process in which radical (chemistry), free radicals "steal" electrons from the lipids in cell membranes, resulting in cell damage. This process proceeds by ...
, improve the photostability of the active ingredients, neutralize reactive oxygen species formed by irradiated photocatalysts ''(eg., uncoated TiO₂)'' and aid in DNA repair post-UVB damage, thus enhancing the efficiency and safety of sunscreens. Compared with sunscreen alone, it has been shown that the addition of antioxidants has the potential to suppress ROS formation by an additional 1.7-fold for SPF 4 sunscreens and 2.4-fold for SPF 15-to-SPF 50 sunscreens, but the efficacy depends on how well the sunscreen in question has been formulated. Sometimes
osmolyte Osmolytes are low-molecular weight organic compounds that influence the properties of biological fluids. Their primary role is to maintain the integrity of cells by affecting the viscosity, melting point, and ionic strength of the aqueous solution. ...
s are also incorporated into commercially available sunscreens in addition to antioxidants since they also aid in protecting the skin from the detrimental effects of UVR. Examples include the osmolyte taurine, which has demonstrated the ability to protects against UVB-radiation induced immunosuppression and the osmolyte ectoine, which aids in counteracting cellular accelerated aging & UVA-radiation induced premature photoaging. Other inactive ingredients can also assist in photostabilizing unstable UV filters.
Cyclodextrin Cyclodextrins are a family of cyclic oligosaccharides, consisting of a macrocyclic ring of glucose subunits joined by α-1,4 glycosidic bonds. Cyclodextrins are produced from starch by enzymatic conversion. They are used in food, pharmaceutical, ...
s have demonstrated the ability to reduce photodecomposition, protect antioxidants and limit skin penetration past the uppermost skin layers, allowing them to longer maintain the protection factor of sunscreens with UV filters that are highly unstable and/or easily permeate to the lower layers of the skin. Similarly, film-forming polymers like polyester-8 and polycryleneS1 have the ability to protect the efficacy of older organic UV filters by preventing them from destabilizing due to extended light exposure. These kinds of ingredients also increase the water resistance of sunscreen formulations. In the 2010s & 2020s there has been increasing interest in sunscreens that protect the wearer from the sun's HEVL &
Infrared light Infrared (IR), sometimes called infrared light, is electromagnetic radiation (EMR) with wavelengths longer than those of visible light. It is therefore invisible to the human eye. IR is generally understood to encompass wavelengths from around ...
as well as ultraviolet light. This is due to newer research revealing blue & violet visible light and certain wavelengths of infrared light ''(eg., NIR, IR-A)'' work synergistically with UV light in contributing to oxidative stress, free radical generation, dermal cellular damage, suppressed skin healing, decreased immunity, erythema, inflammation, dryness, and several aesthetic concerns, such as: wrinkle formation, loss of skin elasticity and dyspigmentation. Increasingly, a number of commercial sunscreens are being produced that have manufacturer claims regarding skin protection from blue light, infrared light and even air pollution. However, as of 2021 there are no regulatory guidelines or mandatory testing protocols that govern these claims. Historically, the American FDA has only recognized protection from sunburn ''(via UVB protection)'' and protection from skin cancer ''(via SPF 15+ with some UVA protection)'' as drug/medicinal sunscreen claims, so they do not have regulatory authority over sunscreen claims regarding protecting the skin from damage from these other environmental stressors. Since sunscreen claims not related to protection from ultraviolet light are treated as
cosmeceutical Cosmeceuticals are cosmetic products with bioactive ingredients purported to have medical benefits. In America, there are no legal requirements to prove that these products live up to their claims. The name is a portmanteau of "cosmetics" and " ...
claims rather than drug/medicinal claims, the innovative technologies and additive ingredients used to allegedly reduce the damage from these other environmental stressors may vary widely from brand to brand. Some studies show that mineral sunscreens primarily made with substantially large particles ''(ie.,neither nano nor micronized)'' may help protect from visible and infrared light to some degree, but these sunscreens are often unacceptable to consumers due to leaving an obligatory opaque white cast on the skin. Further research has shown that sunscreens with added
iron oxide pigments Iron () is a chemical element with symbol Fe (from la, ferrum) and atomic number 26. It is a metal that belongs to the first transition series and group 8 of the periodic table. It is, by mass, the most common element on Earth, right in front ...
and/or pigmentary titanium dioxide can provide the wearer with a substantial amount of HEVL protection. Cosmetic chemists have found that other cosmetic-grade pigments can be functional filler ingredients.
Mica Micas ( ) are a group of silicate minerals whose outstanding physical characteristic is that individual mica crystals can easily be split into extremely thin elastic plates. This characteristic is described as perfect basal cleavage. Mica is ...
was discovered to have significant synergistic effects with UVR filters when formulated in sunscreens, in that it can notably increase the formula's ability to protect the wearer from HEVL. There is a growing amount of research demonstrating that adding various vitamer antioxidants ''(eg;
retinol Retinol, also called vitamin A1, is a fat-soluble vitamin in the vitamin A family found in food and used as a dietary supplement. As a supplement it is used to treat and prevent vitamin A deficiency, especially that which results in xerophtha ...
, alpha tocopherol, gamma tocopherol, tocopheryl acetate,
ascorbic acid Vitamin C (also known as ascorbic acid and ascorbate) is a water-soluble vitamin found in citrus and other fruits and vegetables, also sold as a dietary supplement and as a topical 'serum' ingredient to treat melasma (dark pigment spots) an ...
, ascorbyl tetraisopalmitate, ascorbyl palmitate, sodium ascorbyl phosphate,
ubiquinone Coenzyme Q, also known as ubiquinone and marketed as CoQ10, is a coenzyme family that is ubiquitous in animals and most bacteria (hence the name ubiquinone). In humans, the most common form is coenzyme Q10 or ubiquinone-10. It is a 1,4-benzoq ...
)'' and/or a mixture of certain botanical antioxidants ''(eg;
epigallocatechin-3-gallate Epigallocatechin gallate (EGCG), also known as epigallocatechin-3-gallate, is the ester of epigallocatechin and gallic acid, and is a type of catechin. EGCG – the most abundant catechin in tea – is a polyphenol under basic research for its ...
, b-carotene,
vitis vinifera ''Vitis vinifera'', the common grape vine, is a species of flowering plant, native to the Mediterranean region, Central Europe, and southwestern Asia, from Morocco and Portugal north to southern Germany and east to northern Iran. There are curre ...
,
silymarin Silibinin (International Nonproprietary Name, INN), also known as silybin (both from ''Silybum'', the Genus–differentia definition, generic name of the plant from which it is extracted), is the major active constituent of silymarin, a standard ...
, spirulina extract, chamomile extract and possibly others)'' to sunscreens efficaciously aids in reducing damage from the free radicals produced by exposure to solar ultraviolet radiation, visible light, near infrared radiation and infrared-a radiation. Since sunscreen's active ingredients work preventatively by creating a shielding film on the skin that absorbs, scatters, and reflects light before it can reach the skin, UV filters have been deemed an ideal “first line of defense” against sun damage when exposure can't be avoided. Antioxidants have been deemed a good “second line of defense” since they work responsively by decreasing the overall burden of free radicals that do reach the skin. The degree of the free radical protection from the entire solar spectral range that a sunscreen can offer has been termed the “radical protection factor” (RPF) by some researchers.


Application

SPF 30 or above must be used to effectively prevent UV rays from damaging skin cells. This is the amount that is recommended to prevent against skin cancer. Sunscreen must also be applied thoroughly and re-applied during the day, especially after being in the water. Special attention should be paid to areas like the ears and nose, which are common spots of skin cancer. Dermatologists may be able to advise about what sunscreen is best to use for specific skin types. The dose used in FDA sunscreen testing is 2 mg/cm2 of exposed skin. If one assumes an "average" adult build of height 5 ft 4 in (163 cm) and weight 150 lb (68 kg) with a 32-inch (82-cm) waist, that adult wearing a bathing suit covering the groin area should apply approximately 30 g (or 30 ml, approximately 1 oz) evenly to the uncovered body area. This can be more easily thought of as a "golf ball" size amount of product per body, or at least six teaspoonfuls. Larger or smaller individuals should scale these quantities accordingly. Considering only the face, this translates to about 1/4 to 1/3 of a teaspoon for the average adult face. Some studies have shown that people commonly apply only 1/4 to 1/2 of the amount recommended for achieving the rated sun protection factor (SPF), and in consequence the effective SPF should be downgraded to a 4th root or a square root of the advertised value, respectively. A later study found a significant exponential relation between SPF and the amount of sunscreen applied, and the results are closer to linearity than expected by theory. Claims that substances in pill form can act as sunscreen are false and disallowed in the United States.


Regulation

; Palau On 1 January 2020,
Palau Palau,, officially the Republic of Palau and historically ''Belau'', ''Palaos'' or ''Pelew'', is an island country and microstate in the western Pacific. The nation has approximately 340 islands and connects the western chain of the Caro ...
became the first country in the world to ban sun cream that is harmful to corals and sea life. The ban came into effect immediately after an announcement by President
Tommy Remengesau Jr. Thomas Esang "Tommy" Remengesau Jr. (born 28 February 1956) is a Palauan politician; in 2013 he was elected the ninth president of Palau and was re-elected to that office in 2016. Previously he served as the seventh president of the island nat ...
; United States Sunscreen labeling standards have been evolving in the United States since the FDA first adopted the SPF calculation in 1978. The FDA issued a comprehensive set of rules in June 2011, taking effect in 2012–2013, designed to help consumers identify and select suitable sunscreen products offering protection from sunburn, early skin aging, and skin cancer: * To be classified as "broad spectrum", sunscreen products must provide protection against both
UVA UVA most often refers to: * Ultraviolet A, a type of ultraviolet radiation * University of Virginia, a public research university in Charlottesville, Virginia, United States Uva or UVA may also refer to: Places * Uva, Missouri, an unincorpora ...
and
UVB Ultraviolet (UV) is a form of electromagnetic radiation with wavelength from 10 nm (with a corresponding frequency around 30  PHz) to 400 nm (750  THz), shorter than that of visible light, but longer than X-rays. UV radiation i ...
, with specific tests required for both. * Claims of products being "
waterproof Waterproofing is the process of making an object or structure waterproof or water-resistant so that it remains relatively unaffected by water or resisting the ingress of water under specified conditions. Such items may be used in wet environme ...
" or "sweatproof" are prohibited, while "sunblock" and "instant protection" and "protection for more than 2 hours" are all prohibited without specific FDA approval. * "Water resistance" claims on the front label must indicate how long the sunscreen remains effective and specify whether this applies to swimming or sweating, based on standard testing. * Sunscreens must include standardized "Drug Facts" information on the container. However, there is no regulation that deems it necessary to mention whether the contents contain
nanoparticles A nanoparticle or ultrafine particle is usually defined as a particle of matter that is between 1 and 100 nanometres (nm) in diameter. The term is sometimes used for larger particles, up to 500 nm, or fibers and tubes that are less than 1 ...
of mineral ingredients. (The EU has stricter regulation against the use of nanoparticles, and in 2009 introduced labeling requirements for nanoparticle ingredients in certain sunscreens and cosmetics.) In 2019, the FDA proposed tighter regulations on sun protection and general safety, including the requirement that sunblock products with SPF greater than 15 must be broad spectrum and a prohibition on products with SPF greater than 60. The state of
Hawaii Hawaii ( ; haw, Hawaii or ) is a state in the Western United States, located in the Pacific Ocean about from the U.S. mainland. It is the only U.S. state outside North America, the only state that is an archipelago, and the only stat ...
banned the commercial sale of sunscreens containing oxybenzone and octinoxate on January 1, 2021 due to concern of environmental effects linked to the two ingredients and their contribution to increased coral bleaching. This ban is only applicable to sale within the state and to sunscreen products, not other cosmetic materials. Sunscreen can be purchased using a tax-advantaged health savings account (HSA) or flexible spending account (FSA) in the United States.


Environmental effects

Certain sunscreens in water under ultraviolet light can increase the production of
hydrogen peroxide Hydrogen peroxide is a chemical compound with the formula . In its pure form, it is a very pale blue liquid that is slightly more viscous than water. It is used as an oxidizer, bleaching agent, and antiseptic, usually as a dilute solution (3% ...
, which damages
phytoplankton Phytoplankton () are the autotrophic (self-feeding) components of the plankton community and a key part of ocean and freshwater ecosystems. The name comes from the Greek words (), meaning 'plant', and (), meaning 'wanderer' or 'drifter'. Ph ...
. A 2002 study suggests that sunscreen causes an increase in virus abundance in seawater, leading to poor marine environment health similar to that of other pollutants. A 2008 study that tested different sunscreen brands, protective factors, and concentrations found that they all caused bleaching on hard corals, and the rate of bleaching increased with increased quantity of sunscreen. Of the compounds found in sunscreen that were tested separately, "
butylparaben Butylparaben, or butyl ''p''-hydroxybenzoate, is an organic compound with the formula . It is a white solid that is soluble in organic solvents. It has proven to be a highly successful antimicrobial preservative in cosmetics. It is also used in ...
, ethylhexylmethoxycinnamate, benzophenone-3 and 4-methylbenzylidene camphor caused complete bleaching even at very low concentrations." Media reports link
oxybenzone Oxybenzone or benzophenone-3 or BP-3 (trade names Milestab 9, Eusolex 4360, Escalol 567, KAHSCREEN BZ-3) is an organic compound. It is a pale-yellow solid that is readily soluble in most organic solvents. Oxybenzone belongs to the class of aroma ...
in sunscreens to
coral bleaching Coral bleaching is the process when corals become white due to various stressors, such as changes in temperature, light, or nutrients. Bleaching occurs when coral polyps expel the zooxanthellae (dinoflagellates that are commonly referred to as alg ...
, although some environmental experts dispute the claim. A 2015 study published in the '' Archives of Environmental Contamination and Toxicology'' linked oxybenzone to effects on cell culture experiments and juvenile coral, but other sources of pollution such as agricultural run-off and sewage probably have a larger impact on coral reefs. In 2018, the Pacific nation of Palau has become the first country to ban sun creams containing oxybenzone, octinoxate, and some other harmful elements. A 2019 study of UV filters in oceans found far lower concentrations of oxybenzone than previously reported, and lower than known thresholds for environmental toxicity. Additionally, the
National Oceanic and Atmospheric Administration The National Oceanic and Atmospheric Administration (abbreviated as NOAA ) is an United States scientific and regulatory agency within the United States Department of Commerce that forecasts weather, monitors oceanic and atmospheric conditio ...
(NOAA) has indicated that coral decline is associated with effects from climate change (warming oceans, rising water levels, acidification), overfishing, and pollution from agriculture, wastewater, and urban run-off.


History

Early civilizations used a variety of plant products to help protect the skin from sun damage. For example,
ancient Greeks Ancient Greece ( el, Ἑλλάς, Hellás) was a northeastern Mediterranean civilization, existing from the Greek Dark Ages of the 12th–9th centuries BC to the end of classical antiquity ( AD 600), that comprised a loose collection of cultu ...
used olive oil for this purpose, and ancient Egyptians used extracts of rice, jasmine, and lupine plants whose products are still used in skin care today. Zinc oxide paste has also been popular for skin protection for thousands of years. Among the nomadic sea-going
Sama-Bajau people The Sama-Bajau include several Austronesian ethnic groups of Maritime Southeast Asia. The name collectively refers to related people who usually call themselves the Sama or Samah (formally A'a Sama, "Sama people"); or are known by the exony ...
of the
Philippines The Philippines (; fil, Pilipinas, links=no), officially the Republic of the Philippines ( fil, Republika ng Pilipinas, links=no), * bik, Republika kan Filipinas * ceb, Republika sa Pilipinas * cbk, República de Filipinas * hil, Republ ...
,
Malaysia Malaysia ( ; ) is a country in Southeast Asia. The federation, federal constitutional monarchy consists of States and federal territories of Malaysia, thirteen states and three federal territories, separated by the South China Sea into two r ...
, and
Indonesia Indonesia, officially the Republic of Indonesia, is a country in Southeast Asia and Oceania between the Indian and Pacific oceans. It consists of over 17,000 islands, including Sumatra, Java, Sulawesi, and parts of Borneo and New Guine ...
, a common type of sun protection is a paste called ''borak'' or ''burak'', which was made from water weeds, rice and spices. It is used most commonly by women to protect the face and exposed skin areas from the harsh tropical sun at sea. In
Myanmar Myanmar, ; UK pronunciations: US pronunciations incl. . Note: Wikipedia's IPA conventions require indicating /r/ even in British English although only some British English speakers pronounce r at the end of syllables. As John C. Wells, Joh ...
,
thanaka Thanakha, also spelled Thanakha (; ), is a paste made from ground bark. It is a distinctive feature of the culture of Myanmar, seen commonly applied to the face and sometimes the arms of women and girls, and is used to a lesser extent also by men ...
, a yellow-white cosmetic paste made of ground bark, is traditionally used for sun protection. The first ultraviolet B filters were produced in 1928. Followed by the first sunscreen, invented in Australia by chemist H.A. Milton Blake, in 1932 formulating with the UV filter 'salol' (Phenyl salicylate) at a concentration of 10%. Its protection was verified by the
University of Adelaide The University of Adelaide (informally Adelaide University) is a public research university located in Adelaide, South Australia. Established in 1874, it is the third-oldest university in Australia. The university's main campus is located on N ...
. In 1936, L'Oreal released its first sunscreen product, formulated by French chemist
Eugène Schueller Eugène Paul Louis Schueller (20 March 1881 – 23 August 1957) was a French pharmacist and entrepreneur who was the founder of L'Oréal, the world's leading company in cosmetics and beauty. He was one of the founders of modern advertising. Foun ...
. Early adopters of sunscreen were the US military. In 1944, as the hazards of sun overexposure became apparent to soldiers stationed in the Pacific tropics at the height of
World War II World War II or the Second World War, often abbreviated as WWII or WW2, was a world war that lasted from 1939 to 1945. It involved the vast majority of the world's countries—including all of the great powers—forming two opposin ...
, Benjamin Green, an airman and later a
pharmacist A pharmacist, also known as a chemist (Commonwealth English) or a druggist (North American and, archaically, Commonwealth English), is a healthcare professional who prepares, controls and distributes medicines and provides advice and instructi ...
produced Red Vet Pet (for red veterinary petrolatum) for the US military. Sales boomed when
Coppertone Coppertone is the brand name for an American sunscreen. Coppertone is headquartered in Whippany, New Jersey. Coppertone uses a variety of branding, including the Coppertone girl logo and a distinctive fragrance. Product line The original produ ...
improved and commercialized the substance under the
Coppertone girl Coppertone is the brand name for an American sunscreen. Coppertone is headquartered in Whippany, New Jersey. Coppertone uses a variety of branding, including the Coppertone girl logo and a distinctive fragrance. Product line The original prod ...
and Bain de Soleil branding in the early 1950s. In 1946,
Austria Austria, , bar, Östareich officially the Republic of Austria, is a country in the southern part of Central Europe, lying in the Eastern Alps. It is a federation of nine states, one of which is the capital, Vienna, the most populous ...
n chemist Franz Greiter introduced a product, called ''Gletscher Crème'' (Glacier Cream), subsequently became the basis for the company Piz Buin, named in honor of
the mountain The Mountain (french: La Montagne) was a political group during the French Revolution. Its members, called the Montagnards (), sat on the highest benches in the National Convention. They were the most radical group and opposed the Girondins. Th ...
where Greiter allegedly received the sunburn. In 1974, Greiter adapted earlier calculations from Friedrich Ellinger and Rudolf Schulze and introduced the "sun protection factor" (SPF), which has become the global standard for measuring UVB protection. It has been estimated that ''Gletscher Crème'' had an SPF of 2. Water-resistant sunscreens were introduced in 1977, and recent development efforts have focused on overcoming later concerns by making sunscreen protection both longer-lasting and broader-spectrum, as well as more appealing to use.


Research

New products are in development such as sunscreens based on
bioadhesive Bioadhesives are natural polymeric materials that act as adhesives. The term is sometimes used more loosely to describe a glue formed synthetically from biological monomers such as sugars, or to mean a synthetic material designed to adhere to biolo ...
nanoparticles. These function by encapsulating commercially used UV filters, while being not only adherent to the skin but also non-penetrant. This strategy inhibits primary UV-induced damage as well as secondary free radicals. Additionally, UV rays can pass through glass windows. Therefore it may be wise to wear sunscreen inside homes and cars. Also UV filters based on sinapate
ester In chemistry, an ester is a compound derived from an oxoacid (organic or inorganic) in which at least one hydroxyl group () is replaced by an alkoxy group (), as in the substitution reaction of a carboxylic acid and an alcohol. Glycerides ar ...
s are under study.


References


External links


Does it work, or not?
– illustrated explanation of how UV light is absorbed by chemicals in sunscreen from ''Wired''
56% of Americans Rarely or Never Use Sunscreen
– A survey conducted about the sunscreen habits of modern Americans. {{Authority control Chemical mixtures Australian inventions French inventions Skin care