Homosalate is an

organic compound 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 ...

used in some

sunscreen Sunscreen, also known as sunblock or sun cream, is a photoprotective topical product for the skin that mainly absorbs, or to a much lesser extent reflects, some of the sun's ultraviolet (UV) radiation and thus helps protect against sunburn and ...

s. It is made by the

Fischer–Speier esterification Fischer esterification or Fischer–Speier esterification is a special type of esterification by refluxing a carboxylic acid and an alcohol in the presence of an acid catalyst. The reaction was first described by Emil Fischer and Arthur Speier ...

salicylic acid Salicylic acid is an organic compound with the formula HOC6H4CO2H. A colorless, bitter-tasting solid, it is a precursor to and a metabolite of aspirin (acetylsalicylic acid). It is a plant hormone, and has been listed by the EPA Toxic Substance ...

and 3,3,5-trimethylcyclohexanol, the latter being a

hydrogenated Hydrogenation is a chemical reaction between molecular hydrogen (H2) and another compound or element, usually in the presence of a catalyst such as nickel, palladium or platinum. The process is commonly employed to reduce or saturate organic co ...

derivative of

isophorone Isophorone is an α,β-unsaturated cyclic ketone. It is a colorless liquid with a characteristic peppermint-like odor, although commercial samples can appear yellowish. Used as a solvent and as a precursor to polymers, it is produced on a large ...

. Contained in 45% of U.S. sunscreens, it is used as a chemical UV filter. The salicylic acid portion of the molecule absorbs

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 ...

rays with a wavelength from 295 nm to 315 nm, protecting the skin from sun damage. The

hydrophobic In chemistry, hydrophobicity is the physical property of a molecule that is seemingly repelled from a mass of water (known as a hydrophobe). In contrast, hydrophiles are attracted to water. Hydrophobic molecules tend to be nonpolar and, th ...

trimethyl cyclohexyl group provides greasiness that prevents it from dissolving in water.

Safety

Similar to other UV filter compounds, more homosalate is absorbed into the uppermost stratum corneum (''ie, the stratum disjunctum'') of the face (25% of applied dose) versus back of volunteers. This amounted to approximately two to three times the amount of sunscreen that was present in the superficial

stratum corneum The stratum corneum (Latin for 'horny layer') is the outermost layer of the epidermis. The human stratum corneum comprises several levels of flattened corneocytes that are divided into two layers: the ''stratum disjunctum'' and ''stratum compact ...

layers of the face compared with the back. There was no homosalate detected in the urine samples or

blood plasma Blood plasma is a light amber-colored liquid component of blood in which blood cells are absent, but contains proteins and other constituents of whole blood in suspension. It makes up about 55% of the body's total blood volume. It is the intra ...

samples of the volunteers in this study. Homosalate has been identified as an antiandrogen ''in vitro'', as well as having estrogenic activity toward estrogen receptors α, and general ''in vitro'' estrogenic activity. Homosalate has been shown to be an antagonist toward

androgen An androgen (from Greek ''andr-'', the stem of the word meaning "man") is any natural or synthetic steroid hormone that regulates the development and maintenance of male characteristics in vertebrates by binding to androgen receptors. This inc ...

and

estrogen Estrogen or oestrogen is a category of sex hormone responsible for the development and regulation of the female reproductive system and secondary sex characteristics. There are three major endogenous estrogens that have estrogenic hormonal acti ...

receptors ''

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 ...

''. Some work has shown that organic UV filters in general can present concerns. There is no ''

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 ...

'' evidence of toxicity, endocrine disfunction or adverse effects; and none of these adverse events have ever been reported to occur in humans. An invivo study involving repeated subcutaneous injections of homosalate at dose levels up to 1000mg/kg of body weight to juvenile female Wistar rats over three consecutive days revealed no estrogenic potential in the

uterotrophic The uterus (from Latin ''uterus'', plural ''uteri'') or womb () is the organ in the reproductive system of most female mammals, including humans that accommodates the embryonic and fetal development of one or more embryos until birth. The ut ...

assay. Another study on immature Long-Evans rats receiving up to 892 mg/kg of body weight of homosalate in their daily diet found no estrogenic effects in vivo. Research on

zebra fish The zebrafish (''Danio rerio'') is a freshwater fish belonging to the minnow Family (biology), family (Cyprinidae) of the Order (biology), order Cypriniformes. Native to South Asia, it is a popular aquarium, aquarium fish, frequently sold under ...

also found no estrogenic effects after being continuously exposed to homosalate for 96 hours straight. The SCCS has declared there is no sufficient evidence that identifies pure homosalate as an endocrine disruptor in humans and further declared that invivo research has confirmed that homosalate has no

genotoxic Genotoxicity is the property of chemical agents that damage the genetic information within a cell causing mutations, which may lead to cancer. While genotoxicity is often confused with Mutagen, mutagenicity, all mutagens are genotoxic, but some geno ...

phototoxic Phototoxicity, also called photoirritation, is a chemically induced skin irritation, requiring light, that does not involve the immune system. It is a type of photosensitivity. The skin response resembles an exaggerated sunburn. The involved chemi ...

photosensitive Photosensitivity is the amount to which an object reacts upon receiving photons, especially visible light. In medicine, the term is principally used for abnormal reactions of the skin, and two types are distinguished, photoallergy and phototoxicity. ...

effects when applied topically.

References

{{Salicylates 3,3,5-Trimethylcyclohexyl esters Salicylate esters Sunscreening agents 3-Hydroxypropenals