An eyelash (also called lash) (Latin: ''Cilia'') is one of the hairs that grows at the edge of the eyelids. It grows in one layer on the edge of the upper and lower eyelids. Eyelashes protect the eye from debris, dust, and small particles and perform some of the same functions as whiskers do on a cat or a mouse in the sense that they are sensitive to being touched, thus providing a warning that an object (such as an insect) is near the eye (which then closes reflexively).
The Ancient Greek word for eyelash is βλέφαρον (transliterated as blepharon), which is seen as a root in biological terms like ''
Blephara
''Catocala'' is a generally Holarctic genus of moths in the family Erebidae. The genus was erected by Franz von Paula Schrank in 1802. The moths are commonly known as underwing moths or simply underwings. These terms are sometimes used for a fe ...
''.
Structure
Development
The eyelashes of the human embryo develop from the
ectoderm
The ectoderm is one of the three primary germ layers formed in early embryonic development. It is the outermost layer, and is superficial to the mesoderm (the middle layer) and endoderm (the innermost layer). It emerges and originates from t ...
between the 22nd and 26th week of pregnancy. Natural eyelashes do not grow beyond a certain length, and fall off by themselves without any need for trimming. Eyelashes take about seven to eight weeks to grow back if pulled out, but constant pulling may lead to permanent damage. Their color may differ from that of the hair, although they tend to be dark on someone with dark hair and lighter on someone with light hair. Eyelash hair is not androgenic and is therefore not affected by puberty.
Glands
The
follicles of eyelashes are associated with a number of
gland
In animals, a gland is a group of cells in an animal's body that synthesizes substances (such as hormones) for release into the bloodstream (endocrine gland) or into cavities inside the body or its outer surface (exocrine gland).
Structure
De ...
s known as the
glands of Zeis
Glands of Zeis are unilobar sebaceous glands located on the margin of the eyelid. The glands of Zeis service the eyelash. These glands produce an oily substance that is issued through the excretory ducts of the sebaceous lobule into the middle por ...
and the
glands of Moll
Moll's gland, also known as the gland of Moll or ciliary gland, is a modified apocrine sweat gland that is found on the margin of the eyelid. They are next to the base of the eyelashes, and anterior to the meibomian glands within the distal eyelid ...
.
Clinical significance
There are a number of diseases or disorders involving the eyelashes:
*
Madarosis is the loss of eyelashes.
*
Blepharitis
Blepharitis is one of the most common ocular conditions characterized by inflammation, scaling, reddening, and crusting of the eyelid. This condition may also cause swelling, burning, itching, or a grainy sensation when introducing foreign object ...
is the irritation of the lid margin, where eyelashes join the eyelid. The eyelids are red and itching, the skin often becomes flaky, and the eyelashes may fall out.
*
Distichiasis is the abnormal growth of lashes from certain areas of the eyelid.
*
Trichiasis
Trichiasis ( , ) is a medical term for abnormally positioned eyelashes that grow back toward the eye, touching the cornea or conjunctiva. This can be caused by infection, inflammation, autoimmune conditions, congenital defects, eyelid agenesis and ...
refers to ingrown eyelashes.
*Eyelashes may become infested with parasitic
crab louse
The crab louse or pubic louse (''Pthirus pubis'') is an insect that is an obligate ectoparasite of humans, feeding exclusively on blood. The crab louse usually is found in the person's pubic hair. Although the louse cannot jump, it can also liv ...
.
*An
external hordeolum
A stye, also known as a hordeolum, is a bacterial infection of an oil gland in the eyelid. This results in a red tender bump at the edge of the eyelid. The outside or the inside of the eyelid can be affected.
The cause of a stye is usually a b ...
, or stye, is a
purulent
Pus is an exudate, typically white-yellow, yellow, or yellow-brown, formed at the site of inflammation during bacterial or fungal infection. An accumulation of pus in an enclosed tissue space is known as an abscess, whereas a visible collect ...
inflammation of infected eyelash follicles and surrounding
sebaceous
A sebaceous gland is a microscopic exocrine gland in the skin that opens into a hair follicle to secrete an oily or waxy matter, called sebum, which lubricates the hair and skin of mammals. In humans, sebaceous glands occur in the greatest num ...
(
Gland of Zeis
Glands of Zeis are unilobar sebaceous glands located on the margin of the eyelid. The glands of Zeis service the eyelash. These glands produce an oily substance that is issued through the excretory ducts of the sebaceous lobule into the middle por ...
) and
apocrine
Apocrine () glands are a type of exocrine gland, which are themselves a type of gland, i.e. a group of cells specialized for the release of secretions. Exocrine glands secrete by one of three means: holocrine, merocrine and apocrine. In apocri ...
(
Moll's gland
Moll's gland, also known as the gland of Moll or ciliary gland, is a modified apocrine sweat gland that is found on the margin of the eyelid. They are next to the base of the eyelashes, and anterior to the meibomian glands within the distal eyelid ...
) glands of the lid margin.
*
Trichotillomania
Trichotillomania (TTM), also known as hair-pulling disorder or compulsive hair pulling, is a mental disorder characterized by a long-term urge that results in the pulling out of one's own hair. A brief positive feeling may occur as hair is remov ...
is a disorder that urges the sufferer to pull out
scalp
The scalp is the anatomical area bordered by the human face at the front, and by the neck at the sides and back.
Structure
The scalp is usually described as having five layers, which can conveniently be remembered as a mnemonic:
* S: The ski ...
hair, eyelashes, etc.
*''
Demodex folliculorum
''Demodex folliculorum'' is a microscopic mite that can only survive on the skin of humans. Most people have ''D.folliculorum'' on their skin. Usually, the mites do not cause any harm, so are considered an example of commensalism rather than par ...
'' (or the demodicid) is a small
mite
Mites are small arachnids (eight-legged arthropods). Mites span two large orders of arachnids, the Acariformes and the Parasitiformes, which were historically grouped together in the subclass Acari, but genetic analysis does not show clear e ...
that lives harmlessly in eyelash and other
hair follicle
The hair follicle is an organ found in mammalian skin. It resides in the dermal layer of the skin and is made up of 20 different cell types, each with distinct functions. The hair follicle regulates hair growth via a complex interaction between ...
s, and about 20% of people have these mites living on them. Occasionally they may cause blepharitis.
Eyelash and eyebrow transplant surgeries may help to reconstruct or thicken lashes or eyebrow hair.
Society and culture
Cosmetics
Long eyelashes are considered a sign of
beauty
Beauty is commonly described as a feature of objects that makes these objects pleasurable to perceive. Such objects include landscapes, sunsets, humans and works of art. Beauty, together with art and taste, is the main subject of aesthetics, o ...
in many cultures. Accordingly, some people seek to enhance their eyelash length artificially, using
eyelash extensions
Eyelash extensions are a cosmetics, cosmetic enhancement that involves attaching synthetic or natural hair fibers to the natural Eyelash, eyelashes to create a fuller, more dramatic look. They are applied by a professional using a specialized adhe ...
. On the other hand,
Hadza women are known to trim their own eyelashes.
Kohl
Kohl may refer to:
*Kohl (cosmetics), an ancient eye cosmetic
* Kohl (surname), including a list of people with the surname
*Kohl's
Kohl's (stylized in all caps) is an American department store retail chain, operated by Kohl's Corporation. ...
, a black putty (usually
antimony
Antimony is a chemical element with the symbol Sb (from la, stibium) and atomic number 51. A lustrous gray metalloid, it is found in nature mainly as the sulfide mineral stibnite (Sb2S3). Antimony compounds have been known since ancient ti ...
sulfide or
lead sulfide Lead sulfide refers to two compounds containing lead and sulfur:
* Lead(II) sulfide, PbS, containing lead in the +2 oxidation state, naturally occurring as the mineral galena
*Lead(IV) sulfide
Lead(IV) sulfide is a chemical compound with the formu ...
), has been worn as far back as the
Bronze Age
The Bronze Age is a historic period, lasting approximately from 3300 BC to 1200 BC, characterized by the use of bronze, the presence of writing in some areas, and other early features of urban civilization. The Bronze Age is the second pri ...
to darken the edge of the eyelid (just at the bottom of the eyelashes). In
Ancient Egypt, it was used as well by the wealthy and the royal to beautify their eyes. Modern eye makeup includes
mascara
Mascara is a cosmetic commonly used to enhance the upper and lower eyelashes. It is used to darken, thicken, lengthen, and/or define the eyelashes. Normally in one of three forms—liquid, powder, or cream—the modern mascara product has vari ...
,
eyeliner
Eye liner or eyeliner is a cosmetic used to define the eyes. It is applied around the contours of the eye(s). It is often used to create various aesthetic effects.
History
Eye liner was first used in ancient India, ancient Egypt and Mesopota ...
,
eye putty, and
eye shadow
Eye shadow (or eyeshadow) is a cosmetic applied primarily to the eyelids to attract attention to the wearer's eyes, making them stand out or look more attractive. Eye shadow can also be applied under the eyes, on the cheeks, or to brow bones.
...
to emphasize the eyes. The twentieth century saw the beginning of convincing false eyelashes, popular in the 1960s. There are also different tools that can be used on the lashes such as
eyelash curler
An eyelash curler is a hand-operated mechanical device for curling eyelashes for cosmetic purposes. Usually only the upper eyelashes are curled.
History
There were different patents of this invention between 1923 and 1940. The first known patent ...
or mascara shield (also named mascara guard or eye makeup helper).
Permanent eyelash tints and eyelash extensions have also become popular procedures, even in fairly basic salons. It is also possible to get eyelash transplants, which are similar in nature to
hair transplantation often done on the head. Since the hair is transplanted from the hair on the head, the new eyelashes will continue to grow like head hair and will need to be trimmed regularly.
Latisse was introduced in the first quarter of 2009 by
Allergan
Allergan plc is an American, Irish-domiciled pharmaceutical company that acquires, develops, manufactures and markets brand name drugs and medical devices in the areas of medical aesthetics, eye care, central nervous system, and gastroenterology. ...
as the first drug to receive
FDA approval for eyelash growth. Latisse is a solution of bimatoprost, the active component of the
glaucoma
Glaucoma is a group of eye diseases that result in damage to the optic nerve (or retina) and cause vision loss. The most common type is open-angle (wide angle, chronic simple) glaucoma, in which the drainage angle for aqueous humor, fluid withi ...
medication Lumigan. According to Allergan, noticeable eyelash growth occurs within 16 weeks. Growth is reported to occur primarily on the upper eyelashes. In addition, the past decade has seen the rapid increase in the development of eyelash conditioners. These conditioners are designed to increase the health and length of lashes. Many utilize seed extract, minerals, and other chemicals to achieve these results.
Cosmetic companies have recently relied on scientific research of prostaglandins and the
Wnt/b-catenin signaling pathways to develop eyelash products. Although bimatoprost is effective in promoting increased growth of healthy eyelashes and adnexal hairs, its effectiveness in patients with eyelash alopecia areata is debatable. Some cosmetic brands have begun using
Peptides
Peptides (, ) are short chains of amino acids linked by peptide bonds. Long chains of amino acids are called proteins. Chains of fewer than twenty amino acids are called oligopeptides, and include dipeptides, tripeptides, and tetrapeptides.
...
in their formulation rather than prostaglandins because of regulatory rules in places like Canada and California.
In other animals
Lashes, being hair, are found in
mammal
Mammals () are a group of vertebrate animals constituting the class Mammalia (), characterized by the presence of mammary glands which in females produce milk for feeding (nursing) their young, a neocortex (a region of the brain), fur ...
s.
Camel
A camel (from: la, camelus and grc-gre, κάμηλος (''kamēlos'') from Hebrew or Phoenician: גָמָל ''gāmāl''.) is an even-toed ungulate in the genus ''Camelus'' that bears distinctive fatty deposits known as "humps" on its back. ...
s' lashes are remarkably long and thick.
Horse
The horse (''Equus ferus caballus'') is a domesticated, one-toed, hoofed mammal. It belongs to the taxonomic family Equidae and is one of two extant subspecies of ''Equus ferus''. The horse has evolved over the past 45 to 55 million yea ...
s and
cows feature eyelashes as well. Inherited eyelash problems are common in some breeds of dogs as well as horses.
Eyelashes are an uncommon but not unknown feature in birds.
Hornbills
Hornbills (Bucerotidae) are a family of bird found in tropical and subtropical Africa, Asia and Melanesia. They are characterized by a long, down-curved bill which is frequently brightly coloured and sometimes has a casque on the upper man ...
have prominent eyelashes (
vestigial
Vestigiality is the retention, during the process of evolution, of genetically determined structures or attributes that have lost some or all of the ancestral function in a given species. Assessment of the vestigiality must generally rely on co ...
feathers with no
barbs), as do
ostrich
Ostriches are large flightless birds of the genus ''Struthio'' in the order Struthioniformes, part of the infra-class Palaeognathae, a diverse group of flightless birds also known as ratites that includes the emus, rheas, and kiwis. There ...
es. Amongst the reptiles, only
Eyelash vipers show a set of modified
scales
Scale or scales may refer to:
Mathematics
* Scale (descriptive set theory), an object defined on a set of points
* Scale (ratio), the ratio of a linear dimension of a model to the corresponding dimension of the original
* Scale factor, a number w ...
over the eyes which look much like eyelashes.
See also
*
Eyelash extensions
Eyelash extensions are a cosmetics, cosmetic enhancement that involves attaching synthetic or natural hair fibers to the natural Eyelash, eyelashes to create a fuller, more dramatic look. They are applied by a professional using a specialized adhe ...
, used to enhance the length, curliness, fullness, and thickness of natural eyelashes
References
External links
*
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Facial features