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An eyelash (also called lash) (
Neo-Latin Neo-LatinSidwell, Keith ''Classical Latin-Medieval Latin-Neo Latin'' in ; others, throughout. (also known as New Latin and Modern Latin) is the style of written Latin used in original literary, scholarly, and scientific works, first in Italy d ...
: ''cilium'', plural ''cilia'') is one of the hairs that grows at the edges of the top and bottom
eyelid An eyelid ( ) is a thin fold of skin that covers and protects an eye. The levator palpebrae superioris muscle retracts the eyelid, exposing the cornea to the outside, giving vision. This can be either voluntarily or involuntarily. "Palpebral ...
s, spanning outwards and away from the eyes. The lashes grow in up to six layers on each of the upper and lower eyelids. Eyelashes serve to protect the
eye An eye is a sensory organ that allows an organism to perceive visual information. It detects light and converts it into electro-chemical impulses in neurons (neurones). It is part of an organism's visual system. In higher organisms, the ey ...
from debris, dust, and small particles, and are highly sensitive to touch, thus providing a warning that an object (such as an insect or lint) is near the eye, which then reflexively closes or flutters to rid the area of the object. The eyelid margin from which lashes grow is among the most sensitive parts of the human body, with many nerve endings enveloping the roots of the lashes, giving it sensitivity to very light tactile input even at the tips of the lashes, enabling it to trigger the
blink reflex The corneal reflex, also known as the blink reflex or eyelid reflex, is an involuntary blinking of the eyelids elicited by stimulation of the cornea (such as by touching or by a foreign body), though it could result from any peripheral stimulus ...
when touched. Eyelashes are also an important component of physical attractiveness, with long prominent lashes giving the illusion of large, gazing eyes, and drawing attention to the eyes.


Etymology

The word ''eyelash'' is a compound consisting of the words ''eye'', referring to the eye which the lashes surround and protect; and ''lash'', referring to the braided cord of a
whip A whip is a blunt weapon or implement used in a striking motion to create sound or pain. Whips can be used for flagellation against humans or animals to exert control through pain compliance or fear of pain, or be used as an audible cue thro ...
or to the act of stroking with a whip. This is in reference to both the individual lashes resembling whips, and the action of blinking the eyes causing the lashes to move in a stroking or whipping motion.


Function

In humans, the eyelashes serve four main functions: # Protect the eye from dust and debris by catching them before they can enter the eye # Trigger the
blink reflex The corneal reflex, also known as the blink reflex or eyelid reflex, is an involuntary blinking of the eyelids elicited by stimulation of the cornea (such as by touching or by a foreign body), though it could result from any peripheral stimulus ...
in the case of a foreign body approaching the eye and touching the lashes # Regulate or reduce evaporation of the tear film on the
cornea The cornea is the transparency (optics), transparent front part of the eyeball which covers the Iris (anatomy), iris, pupil, and Anterior chamber of eyeball, anterior chamber. Along with the anterior chamber and Lens (anatomy), lens, the cornea ...
# Protect the
conjunctiva In the anatomy of the eye, the conjunctiva (: conjunctivae) is a thin mucous membrane that lines the inside of the eyelids and covers the sclera (the white of the eye). It is composed of non-keratinized, stratified squamous epithelium with gobl ...
e from excessive light and
ultraviolet Ultraviolet radiation, also known as simply UV, is electromagnetic radiation of wavelengths of 10–400 nanometers, shorter than that of visible light, but longer than X-rays. UV radiation is present in sunlight and constitutes about 10% of ...
radiation, by forming a filamentous curtain-like structure through their arrangement in multiple imperfect rows


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 the o ...
between the 22nd and 26th week of pregnancy. 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 Hair is a protein filament that grows from follicles found in the dermis. Hair is one of the defining characteristics of mammals. The human body, apart from areas of glabrous skin, is covered in follicles which produce thick terminal and ...
, 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. Lash follicles do not have an arrector pili muscle associated with them, making the lashes static.


Length

Human eyelash length is the subject of extensive studies, both for the effect on their functional efficacy, and for their effect on human physical attractiveness. This is also because lashes do not continually grow to long lengths like
scalp The scalp is the area of the head where head hair grows. It is made up of skin, layers of connective and fibrous tissues, and the membrane of the skull. Anatomically, the scalp is part of the epicranium, a collection of structures covering th ...
hair, and the individual variability in their length is almost solely determined by
genetics Genetics is the study of genes, genetic variation, and heredity in organisms.Hartl D, Jones E (2005) It is an important branch in biology because heredity is vital to organisms' evolution. Gregor Mendel, a Moravian Augustinians, Augustinian ...
. While there is considerable variation in the length of lashes between individuals (3 mm to 10 mm for upper lashes), lashes do not vary in length by
sex Sex is the biological trait that determines whether a sexually reproducing organism produces male or female gametes. During sexual reproduction, a male and a female gamete fuse to form a zygote, which develops into an offspring that inheri ...
or
ethnicity An ethnicity or ethnic group is a group of people with shared attributes, which they Collective consciousness, collectively believe to have, and long-term endogamy. Ethnicities share attributes like language, culture, common sets of ancestry, ...
, with the upper lashes of humans typically 7 to 8 mm in length regardless of sex, and generally do not exceed 10 mm in length. Thus, the lashes of humans are considered to be remarkably long when they are 10 mm or greater in length. Lower lashes average between 5 and 6 mm in length. In trichomegaly, the lashes may grow exceptionally long (occasionally 15 mm for the upper lashes). The longest lashes usually grow from the centre of the eyelid. Human eyelash length, thickness, and darkness decrease significantly with age, hence long and thick lashes are sometimes seen as a mark of fertility and youthfulness. Eyelash length is closely linked to the width of the eye, with the lashes typically growing to one-third the width of the eye as an evolutionary adaptation to reduce tear film evaporation and dust deposition. Lashes longer or shorter than one-third the width of the eye have been shown to have reduced efficacy in serving their function. The typical width of the human eye is 24.2 mm, resulting in the average human eyelash length of 7 to 8 mm. This evolutionary trait is perhaps why lashes in humans rarely grow beyond 10 mm in length. However, longer lashes offer more protection against ultraviolet radiation than their shorter counterparts.


Thickness

Lashes grow thick at the roots, and have tapered ends. People of Asian ethnicities have significantly thicker lashes, with an average lash diameter of 71.7 μm, than people of Caucasian ethnicities, with have an average lash diameter of 61.0 μm. However, the number of lashes on the eyelids is fewer in Asians, who typically have 150 lash hairs on the upper lids, than in Caucasians, who typically have 170 lash hairs on the upper lid.


Curvature

Eyelashes grow outwards from both upper and lower eyelids, with varying degrees of curl. People of Caucasian ethnicities have lashes that are more curled than those of Asian ethnicities. However, the degree of curling varies significantly even within a population or ethnicity, where people of Asian ethnicities can also exhibit naturally highly curled lashes.


Density

The number of individual lashes on the upper eyelid is typically 90 to 160, and on the lower eyelid 75 to 80. The number of follicles and hence lashes cannot be increased after birth because all follicles develop during embryogenesis.


Glands

The follicles of eyelashes are associated with a number of
gland A gland is a Cell (biology), cell or an Organ (biology), organ in an animal's body that produces and secretes different substances that the organism needs, either into the bloodstream or into a body cavity or outer surface. A gland may also funct ...
s known as the glands of Zeis and the glands of Moll. At the edge of the eyelid, the Meibomian Gland is located as an oil-producing gland, maintaining the health and function of the eyelashes.


Clinical significance

There are a number of diseases or disorders involving the eyelashes: * Madarosis is the loss of eyelashes. *
Blepharitis Blepharitis, sometimes known as granulated eyelids, 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 ...
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 an ...
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 parasite, obligate Parasitism#Basic concepts, ectoparasite of humans, feeding exclusively on blood. The crab louse usually is found in the person's pubic hair. A ...
. *An external hordeolum, or stye, is a purulent inflammation of infected eyelash follicles and surrounding
sebaceous A sebaceous gland or oil 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 t ...
( Gland of Zeis) and
apocrine Apocrine () is a term used to classify the mode of secretion of exocrine glands. In apocrine secretion, secretory cells accumulate material at their apical ends, often forming blebs or "snouts", and this material then buds off from the cells ...
( Moll's gland) 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 rem ...
is a disorder that urges the sufferer to pull out
scalp The scalp is the area of the head where head hair grows. It is made up of skin, layers of connective and fibrous tissues, and the membrane of the skull. Anatomically, the scalp is part of the epicranium, a collection of structures covering th ...
hair, eyelashes, etc. *''
Demodex folliculorum ''Demodex folliculorum'' is a microscopic mite that can survive only on the skin of humans. Most people host ''D.folliculorum'' on their skin particularly on the face, where sebaceous glands are most concentrated. Usually, the mites do not caus ...
'' (or the demodicid) is a small
mite Mites are small arachnids (eight-legged arthropods) of two large orders, the Acariformes and the Parasitiformes, which were historically grouped together in the subclass Acari. However, most recent genetic analyses do not recover the two as eac ...
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 betwee ...
s, and about 20% of people have these mites living on them. Occasionally they may cause blepharitis. *People with vernal keratoconjunctivitis have longer eyelashes, with the increased growth likely a result of the occular inflammation accompanying the condition. * Trichomegaly is the condition of abnormally long and/or lush lashes (the objective criteria being lashes of 12 mm or greater in length on the upper eyelids). Eyelash transplant surgeries may help to reconstruct lost or damaged lashes. The procedure may also be employed to increase the number of lash follicles on the eyelid to enhance the prominence and fullness of the lashes. The transplanted hairs usually do not have the tapered structure of real lashes, and continue to grow at the same rate as hairs from the area the follicle was extracted from. As such, they require maintenance by means of trimming.


Society and culture

Prominent, luscious eyelashes have long been considered a sign of
beauty Beauty is commonly described as a feature of objects that makes them pleasure, pleasurable to perceive. Such objects include landscapes, sunsets, humans and works of art. Beauty, art and taste are the main subjects of aesthetics, one of the fie ...
in many cultures, almost universally, and as such are highly coveted, particularly by women. Having longer and thicker lashes can also have a positive
psychological Psychology is the scientific study of mind and behavior. Its subject matter includes the behavior of humans and nonhumans, both consciousness, conscious and Unconscious mind, unconscious phenomena, and mental processes such as thoughts, feel ...
effect on women. Despite not varying by sex and not being a
secondary sex characteristic A secondary sex characteristic is a physical characteristic of an organism that is related to or derived from its sex, but not directly part of its reproductive system. In humans, these characteristics typically start to appear during pubert ...
, long, prominent lashes are frequently considered a feminine trait, with studies showing that women possessing longer lashes are perceived as healthier and more feminine. Nevertheless, long lashes are regarded as an attractive
facial feature The face is the front of the head that features the eyes, nose and mouth, and through which animals express many of their emotions. The face is crucial for human identity, and damage such as scarring or developmental deformities may affect ...
in both males and females. On the other hand, Hadza women are known to trim their own eyelashes. Nonetheless, an average length eyelash is considered the most attractive across Asian, Indian, Black and White faces.
Ancient Romans The Roman people was the ethnicity and the body of Roman citizenship, Roman citizens (; ) during the Roman Kingdom, the Roman Republic, and the Roman Empire. This concept underwent considerable changes throughout the long history of the Roman ...
considered long eyelashes a component of aesthetically ideal eyes.
Pliny the Elder Gaius Plinius Secundus (AD 23/24 79), known in English as Pliny the Elder ( ), was a Roman Empire, Roman author, Natural history, naturalist, and naval and army commander of the early Roman Empire, and a friend of the Roman emperor, emperor Vesp ...
wrote that eyelashes fell out from sexual excess, so women desired long lashes as a symbol of chastity. This may have had medical basis as a symptom of
syphilis Syphilis () is a sexually transmitted infection caused by the bacterium ''Treponema pallidum'' subspecies ''pallidum''. The signs and symptoms depend on the stage it presents: primary, secondary, latent syphilis, latent or tertiary. The prim ...
is often
alopecia Hair loss, also known as alopecia or baldness, refers to a loss of hair from part of the head or body. Typically at least the head is involved. The severity of hair loss can vary from a small area to the entire body. Inflammation or scarring ...
of the lashes, suggesting that individuals with short or sparse lashes were sexually promiscuous. The traditional Meitei writing system has two letters (symbols), related to eyelashes. The letter "ꯄ" ("Paa") symbolises the human eyelash, and its letter name "Paa" itself means "eyelash" in
Meitei language Meitei (; ) also known as Manipuri ), is a Tibeto-Burman language of northeast India. It is the official language and the lingua franca of Manipur and an additional official language in four districts of Assam. It is one of the scheduled ...
. It has an additional form of letter, known as "Pa Lonsum" ("ꯞ").


Nonverbal communication

The lashes and lids play a role in
eye contact Eye contact occurs when two people or non-human animals look at each other's eyes at the same time. In people, eye contact is a form of nonverbal communication and can have a large influence on social behavior. Coined in the early to mid-1960s, ...
and
nonverbal communication Nonverbal communication is the transmission of messages or signals through a nonverbal platform such as eye contact (oculesics), body language (kinesics), social distance (proxemics), touch (Haptic communication, haptics), voice (prosody (lingui ...
. Voluntarily blinking slowly or a few times in succession quickly is a feminine flirtatious behaviour commonly referred to as to "bat an eyelash", "bat/batting eyelashes", or "flutter/fluttering eyelashes".


Cosmetics

Because long eyelashes are aesthetically pleasing and seen as a desirable trait that adds to physical attractiveness, some people seek to enhance their eyelash length artificially, by means of eyelash extensions, false lashes attached to the eyelid, cosmetics, or growth products. Additionally, eyelashes which are curled are also more prominent, being able to better display their length especially when viewed from the front. The enhanced appearance of curled eyelashes can be cosmetically achieved by use of eyelash curlers, or eyelash perms. However, these methods do not physically lengthen the lashes. Kohl, a black putty (usually
antimony Antimony is a chemical element; it has chemical symbol, symbol Sb () and atomic number 51. A lustrous grey metal or metalloid, it is found in nature mainly as the sulfide mineral stibnite (). Antimony compounds have been known since ancient t ...
sulfide or lead sulfide), has been worn as far back as the
Bronze Age The Bronze Age () was a historical period characterised principally by the use of bronze tools and the development of complex urban societies, as well as the adoption of writing in some areas. The Bronze Age is the middle principal period of ...
to darken the edge of the eyelid (just at the bottom of the eyelashes). In
Ancient Egypt Ancient Egypt () was a cradle of civilization concentrated along the lower reaches of the Nile River in Northeast Africa. It emerged from prehistoric Egypt around 3150BC (according to conventional Egyptian chronology), when Upper and Lower E ...
, it was used as well by the wealthy and the royal to beautify their eyes. Modern eye makeup includes
mascara Mascara (, ) is a Cosmetics, 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 p ...
, eyeliner, 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. 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 Hair transplantation is a surgery, surgical technique that removes hair follicles from one part of the body, called the 'donor site', to a bald or balding part of the body known as the 'recipient site'. The technique is primarily used to treat ...
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 The United States Food and Drug Administration (FDA or US FDA) is a federal agency of the Department of Health and Human Services. The FDA is responsible for protecting and promoting public health through the control and supervision of food ...
approval for eyelash growth. Latisse is a solution of bimatoprost, a
prostaglandin Prostaglandins (PG) are a group of physiology, physiologically active lipid compounds called eicosanoids that have diverse hormone-like effects in animals. Prostaglandins have been found in almost every Tissue (biology), tissue in humans and ot ...
analog and the active component of the
glaucoma Glaucoma is a group of eye diseases that can lead to damage of the optic nerve. The optic nerve transmits visual information from the eye to the brain. Glaucoma may cause vision loss if left untreated. It has been called the "silent thief of ...
medication Lumigan. According to Allergan, noticeable eyelash growth occurs within 16 weeks. Growth is reported to occur primarily on the upper eyelashes, with as much as a 25% increase in length. 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. A polypeptide is a longer, continuous, unbranched peptide chain. Polypeptides that have a molecular mass of 10,000 Dalton (unit), Da or more are called proteins. Chains of fewer t ...
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 A mammal () is a vertebrate animal of the Class (biology), class Mammalia (). Mammals are characterised by the presence of milk-producing mammary glands for feeding their young, a broad neocortex region of the brain, fur or hair, and three ...
s.
Camel A camel (from and () from Ancient Semitic: ''gāmāl'') is an even-toed ungulate in the genus ''Camelus'' that bears distinctive fatty deposits known as "humps" on its back. Camels have long been domesticated and, as livestock, they provid ...
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 mi ...
s and
cow Cattle (''Bos taurus'') are large, domesticated, bovid ungulates widely kept as livestock. They are prominent modern members of the subfamily Bovinae and the most widespread species of the genus '' Bos''. Mature female cattle are called co ...
s 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 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. Two living species are recognised, the common ostrich, native to large parts of sub-Saharan Africa, and the Somali ostrich, native to the Horn of Africa. They are the heaviest and largest living birds, w ...
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 ...
over the eyes which look much like eyelashes.


See also

* Eyelash extensions, used to enhance the appearance of length, curliness, fullness, and thickness of natural eyelashes *
Eyebrow An eyebrow is an area of short hairs above each eye that follows the shape of the lower margin of the Supraorbital ridge, brow ridges of some mammals. In humans, eyebrows serve two main functions: first, human communication, communication thro ...
s, an area of short hairs above the eyes on the brow ridges


References


External links

* {{Use dmy dates, date=April 2017 Facial features