For other uses, see Hair (disambiguation).
"Hairy" redirects here.
For the epithet, see List of people known as the Hairy.
For the gene, see Hairy (gene).
"Glabrousness" redirects here.
For other uses, see Glabrousness (disambiguation).
Not to be confused with Fur.
Hair is one of the defining characteristics of mammals.
Attitudes towards different forms of hair, such as hairstyles and hair removal, vary widely across different cultures and historical periods, but it is often used to indicate a person's personal beliefs or social position, such as their age, sex, or religion.
The word "hair" usually refers to two distinct structures:
- the part beneath the skin, called the hair follicle, or, when pulled from the skin, the bulb or root. This organ is located in the dermis and maintains stem cells, which not only re-grow the hair after it falls out, but also are recruited to regrow skin after a wound.
- the shaft, which is the hard filamentous part that extends above the skin surface. A cross section of the hair shaft may be divided roughly into three zones.
Hair fibers have a structure consisting of several layers, starting from the outside:
- the cuticle, which consists of several layers of flat, thin cells laid out overlapping one another as roof shingles
- the cortex, which contains the keratin bundles in cell structures that remain roughly rod-like
- the medulla, a disorganized and open area at the fiber's center
The innermost region, the medulla, is not always present and is an open, unstructured region.
The highly structural and organized cortex, or second of three layers of the hair, is the primary source of mechanical strength and water uptake.
The shape of the follicle determines the shape of the cortex, and the shape of the fiber is related to how straight or curly the hair is.
People with straight hair have round hair fibers.
Oval and other shaped fibers are generally more wavy or curly.
The cuticle is the outer covering.
Its complex structure slides as the hair swells and is covered with a single molecular layer of lipid that makes the hair repel water.
The diameter of human hair varies from 0.017 to 0.18 millimeters (0.00067 to 0.00709 in).
There are two million small, tubular glands and sweat glands that produce watery fluids that cool the body by evaporation.
The glands at the opening of the hair produce a fatty secretion that lubricates the hair.
Hair growth begins inside the hair follicle.
The only "living" portion of the hair is found in the follicle.
The hair that is visible is the hair shaft, which exhibits no biochemical activity and is considered "dead".
The base of a hair's root (the "bulb") contains the cells that produce the hair shaft.
In humans with little body hair, the effect results in goose bumps.
Root of the hair
|Root of the hair|
The root of the hair ends in an enlargement, the hair bulb, which is whiter in color and softer in texture than the shaft, and is lodged in a follicular involution of the epidermis called the hair follicle.
The bulb of hair consists of fibrous connective tissue, glassy membrane, external root sheath, internal root sheath composed of epithelium stratum (Henle's layer) and granular stratum (Huxley's layer), cuticle, cortex and medulla.
Main article: Human hair color
All natural hair colors are the result of two types of hair pigments.
Both of these pigments are melanin types, produced inside the hair follicle and packed into granules found in the fibers.
Gray hair occurs when melanin production decreases or stops, while poliosis is hair (and often the skin to which the hair is attached), typically in spots, that never possessed melanin at all in the first place, or ceased for natural genetic reasons, generally, in the first years of life.
Human hair growth
Main article: Human hair growth
Hair grows everywhere on the external body except for mucus membranes and glabrous skin, such as that found on the palms of the hands, soles of the feet, and lips.
Each has specific characteristics that determine the length of the hair.
The different construction gives the hair unique characteristics, serving specific purposes, mainly, warmth and protection.
Hair exists in a variety of textures.
Three main aspects of hair texture are the curl pattern, volume, and consistency.
The derivations of hair texture are not fully understood.
There are a range of theories pertaining to the curl patterns of hair.
Scientists have come to believe that the shape of the hair shaft has an effect on the curliness of the individual's hair.
A very round shaft allows for fewer disulfide bonds to be present in the hair strand.
This means the bonds present are directly in line with one another, resulting in straight hair.
The flatter the hair shaft becomes, the curlier hair gets, because the shape allows more cysteines to become compacted together resulting in a bent shape that, with every additional disulfide bond, becomes curlier in form.
As the hair follicle shape determines curl pattern, the hair follicle size determines thickness.
While the circumference of the hair follicle expands, so does the thickness of the hair follicle.
An individual's hair volume, as a result, can be thin, normal, or thick.
The consistency of hair can almost always be grouped into three categories: fine, medium, and coarse.
This trait is determined by the hair follicle volume and the condition of the strand.
Fine hair has the smallest circumference, coarse hair has the largest circumference, and medium hair is anywhere between the other two.
Coarse hair has a more open cuticle than thin or medium hair causing it to be the most porous.
There are various systems that people use to classify their curl patterns.
Being knowledgeable of an individual's hair type is a good start to knowing how to take care of one's hair.
There is not just one method to discovering one's hair type.
Additionally it is possible, and quite normal to have more than one kind of hair type, for instance having a mixture of both type 3a & 3b curls.
The Andre Walker Hair Typing System is the most widely used system to classify hair.
According to this system there are four types of hair: straight, wavy, curly, kinky.
- Type 1 is straight hair, which reflects the most sheen and also the most resilient hair of all of the hair types. It is hard to damage and immensely difficult to curl this hair texture. Because the sebum easily spreads from the scalp to the ends without curls or kinks to interrupt its path, it is the most oily hair texture of all.
- Type 2 is wavy hair, whose texture and sheen ranges somewhere between straight and curly hair. Wavy hair is also more likely to become frizzy than straight hair. While type A waves can easily alternate between straight and curly styles, type B and C Wavy hair is resistant to styling.
- Type 3 is curly hair known to have an S-shape. The curl pattern may resemble a lowercase "s", uppercase "S", or sometimes an uppercase "Z" or lowercase "z". This hair type is usually voluminous, "climate dependent (humidity = frizz), and damage-prone." Lack of proper care causes less defined curls.
- Type 4 is kinky hair, which features a tightly coiled curl pattern (or no discernible curl pattern at all) that is often fragile with a very high density. This type of hair shrinks when wet and because it has fewer cuticle layers than other hair types it is more susceptible to damage.
|Type 1: Straight|
|1a||Straight (Fine/Thin)||Hair tends to be very soft, thin, shiny, oily, poor at holding curls, difficult to damage.|
|1b||Straight (Medium)||Hair characterized by volume and body.|
|1c||Straight (Coarse)||Hair tends to be bone-straight, coarse, difficult to curl.|
|Type 2: Wavy|
|2a||Wavy (Fine/Thin)||Hair has definite "S" pattern, can easily be straightened or curled, usually receptive to a variety of styles.|
|2b||Wavy (Medium)||Can tend to be frizzy and a little resistant to styling.|
|2c||Wavy (Coarse)||Fairly coarse, frizzy or very frizzy with thicker waves, often more resistant to styling.|
|Type 3: Curly|
|3a||Curly (Loose)||Presents a definite "S" pattern, tends to combine thickness, volume, and/or frizziness.|
|3b||Curly (Tight)||Presents a definite "S" pattern, curls ranging from spirals to spiral-shaped corkscrew|
|Type 4: Kinky|
|4a||Kinky (Soft)||Hair tends to be very wiry and fragile, tightly coiled and can feature curly patterning.|
|4b||Kinky (Wiry)||As 4a but with less defined pattern of curls, looks more like a "Z" with sharp angles|
This is a method which classifies the hair by curl pattern, hair-strand thickness and overall hair volume.
|1b||Straight but with a slight body wave adding some volume.|
|1c||Straight with body wave and one or two visible S-waves (e.g. at nape of neck or temples).|
|2a||Loose with stretched S-waves throughout.|
|2b||Shorter with more distinct S-waves (resembling e.g. braided damp hair).|
|2c||Distinct S-waves, some spiral curling.|
|3a||Big, loose spiral curls.|
|Very ("Really") curly|
|4a||Tightly coiled S-curls.|
|4b||Z-patterned (tightly coiled, sharply angled)|
|4c||Mostly Z-patterned (tightly kinked, less definition)|
Thin strands that sometimes are almost translucent when held up to the light. Shed strands can be hard to see even against a contrasting background. Fine hair is difficult to feel or it feels like an ultra-fine strand of silk.
Strands are neither fine nor coarse. Medium hair feels like a cotton thread, but isn't stiff or rough. It is neither fine nor coarse.
Thick strands whose shed strands usually are easily identified. Coarse hair feels hard and wiry.
by circumference of full-hair ponytail
|i||Thin||circumference less than 2 inches (5 centimetres)|
|ii||Normal||... from 2 to 4 inches (5 to 10 centimetres)|
|iii||Thick||... more than 4 inches (10 centimetres)|
Many mammals have fur and other hairs that serve different functions.
Hair provides thermal regulation and camouflage for many animals; for others it provides signals to other animals such as warnings, mating, or other communicative displays; and for some animals hair provides defensive functions and, rarely, even offensive protection.
Hair also has a sensory function, extending the sense of touch beyond the surface of the skin.
Guard hairs give warnings that may trigger a recoiling reaction.
While humans have developed clothing and other means of keeping warm, the hair found on the head serves primarily as a source of heat insulation and cooling (when sweat evaporates from soaked hair) as well as protection from ultra-violet radiation exposure.
The function of hair in other locations is debated.
Hats and coats are still required while doing outdoor activities in cold weather to prevent frostbite and hypothermia, but the hair on the human body does help to keep the internal temperature regulated.
When the body is too cold, the arrector pili muscles found attached to hair follicles stand up, causing the hair in these follicles to do the same.
These hairs then form a heat-trapping layer above the epidermis.
This is more effective in other mammals whose fur fluffs up to create air pockets between hairs that insulate the body from the cold.
The opposite actions occur when the body is too warm; the arrector muscles make the hair lie flat on the skin which allows heat to leave.
These are covered with thick plates of keratin and serve as protection against predators.
Thick hair such as that of the lion's mane and grizzly bear's fur do offer some protection from physical damages such as bites and scratches.
Displacement and vibration of hair shafts are detected by hair follicle nerve receptors and nerve receptors within the skin.
Hairs can sense movements of air as well as touch by physical objects and they provide sensory awareness of the presence of ectoparasites.
Some hairs, such as eyelashes, are especially sensitive to the presence of potentially harmful matter.
Eyebrows and eyelashes
They also play a key role in non-verbal communication by displaying emotions such as sadness, anger, surprise and excitement.
In many other mammals, they contain much longer, whisker-like hairs that act as tactile sensors.
The eyelash grows at the edges of the eyelid and protects the eye from dirt.
The eye reflexively closes as a result of this sensation.
Hair has its origins in the common ancestor of mammals, the synapsids, about 300 million years ago.
An exceptionally well-preserved skull of Estemmenosuchus, a therapsid from the Upper Permian, shows smooth, hairless skin with what appears to be glandular depressions, though as a semi-aquatic species it might not have been particularly useful to determine the integument of terrestrial species.
If this is the case, these are the oldest hair remnants known, showcasing that fur occurred as far back as the latest Paleozoic.
The hairs of the fur in modern animals are all connected to nerves, and so the fur also serves as a transmitter for sensory input.
Fur could have evolved from sensory hair (whiskers).
A full pelage likely did not evolve until the therapsid-mammal transition.
The high interspecific variability of the size, color, and microstructure of hair often enables the identification of species based on single hair filaments.
In varying degrees most mammals have some skin areas without natural hair.
On the human body, glabrous skin is found on the ventral portion of the fingers, palms, soles of feet and lips, which are all parts of the body most closely associated with interacting with the world around us, as are the labia minora and glans penis.
The naked mole-rat (Heterocephalus glaber) has evolved skin lacking in general, pelagic hair covering, yet has retained long, very sparsely scattered tactile hairs over its body.
Glabrousness is a trait that may be associated with neoteny.
The general hairlessness of humans in comparison to related species may be due to loss of functionality in the pseudogene KRTHAP1 (which helps produce keratin) in the human lineage about 240,000 years ago.
On an individual basis, mutations in the gene HR can lead to complete hair loss, though this is not typical in humans.
Humans may also lose their hair as a result of hormonal imbalance due to drugs or pregnancy.
In order to comprehend why humans are essentially hairless, it is essential to understand that mammalian body hair is not merely an aesthetic characteristic; it protects the skin from wounds, bites, heat, cold, and UV radiation.
Additionally, it can be used as a communication tool and as a camouflage.
To this end, it can be concluded that benefits stemming from the loss of human body hair must be great enough to outweigh the loss of these protective functions by nakedness.
Humans are the only primate species that have undergone significant hair loss and of the approximately 5000 extant species of mammal, only a handful are effectively hairless.
Most mammals have light skin that is covered by fur, and biologists believe that early human ancestors started out this way also.
Therefore, evidence of the time when human skin darkened has been used to date the loss of human body hair, assuming that the dark skin was needed after the fur was gone.
However, it turned out that the human pubic louse does not descend from the ancestral human louse, but from the gorilla louse, diverging 3.3 million years ago.
This suggests that humans had lost body hair (but retained head hair) and developed thick pubic hair prior to this date, were living in or close to the forest where gorillas lived, and acquired pubic lice from butchering gorillas or sleeping in their nests.
The evolution of the body louse from the head louse, on the other hand, places the date of clothing much later, some 100,000 years ago.
The sweat glands in humans could have evolved to spread from the hands and feet as the body hair changed, or the hair change could have occurred to facilitate sweating.
Horses and humans are two of the few animals capable of sweating on most of their body, yet horses are larger and still have fully developed fur.
In humans, the skin hairs lie flat in hot conditions, as the arrector pili muscles relax, preventing heat from being trapped by a layer of still air between the hairs, and increasing heat loss by convection.
Another hypothesis for the thick body hair on humans proposes that Fisherian runaway sexual selection played a role (as well as in the selection of long head hair), (see terminal and vellus hair), as well as a much larger role of testosterone in men.
Sexual selection is the only theory thus far that explains the sexual dimorphism seen in the hair patterns of men and women.
On average, men have more body hair than women.
The halting of hair development at a juvenile stage, vellus hair, would also be consistent with the neoteny evident in humans, especially in females, and thus they could have occurred at the same time.
This theory, however, has significant holdings in today's cultural norms.
There is no evidence that sexual selection would proceed to such a drastic extent over a million years ago when a full, lush coat of hair would most likely indicate health and would therefore be more likely to be selected for, not against, and not all human populations today have sexual dimorphism in body hair.
A further hypothesis is that human hair was reduced in response to ectoparasites.
The "ectoparasite" explanation of modern human nakedness is based on the principle that a hairless primate would harbor fewer parasites.
When our ancestors adopted group-dwelling social arrangements roughly 1.8 mya, ectoparasite loads increased dramatically.
Early humans became the only one of the 193 primate species to have fleas, which can be attributed to the close living arrangements of large groups of individuals.
While primate species have communal sleeping arrangements, these groups are always on the move and thus are less likely to harbor ectoparasites.
Because of this, selection pressure for early humans would favor decreasing body hair because those with thick coats would have more lethal-disease-carrying ectoparasites and would thereby have lower fitness.
Giles also connects romantic love to hairlessness.
Another hypothesis is that humans' use of fire caused or initiated the reduction in human hair.
They devised new hunting techniques.
The higher protein diet led to the evolution of larger body and brain sizes.
Jablonski postulates that increasing body size, in conjunction with intensified hunting during the day at the equator, gave rise to a greater need to rapidly expel heat.
As a result, humans evolved the ability to sweat: a process which was facilitated by the loss of body hair.
Another factor in human evolution that also occurred in the prehistoric past was a preferential selection for neoteny, particularly in females.
The idea that adult humans exhibit certain neotenous (juvenile) features, not evinced in the great apes, is about a century old.
For instance, vellus hair is a juvenile characteristic.
Further information: Human evolutionary genetics
The EDAR locus
A group of studies have recently shown that genetic patterns at the EDAR locus, a region of the modern human genome that contributes to hair texture variation among most individuals of East Asian descent, support the hypothesis that (East Asian) straight hair likely developed in this branch of the modern human lineage subsequent to the original expression of tightly coiled natural afro-hair.
Specifically, the relevant findings indicate that the EDAR mutation coding for the predominant East Asian 'coarse' or thick, straight hair texture arose within the past ≈65,000 years, which is a time frame that covers from the earliest of the 'Out of Africa' migrations up to now.
See also: Hair diseases
Premature greying of hair is another condition that results in greying before the age of 20 years in Whites, before 25 years in Asians, and before 30 years in Africans.
Main article: Hair care
Hair care routines differ according to an individual's culture and the physical characteristics of one's hair.
Hair may be colored, trimmed, shaved, plucked, or otherwise removed with treatments such as waxing, sugaring, and threading.
Depilation is the removal of hair from the surface of the skin.
This can be achieved through methods such as shaving.
Epilation is the removal of the entire hair strand, including the part of the hair that has not yet left the follicle.
A popular way to epilate hair is through waxing.
The blade is brought close to the skin and stroked over the hair in the desired area to cut the terminal hairs and leave the skin feeling smooth.
Depending upon the rate of growth, one can begin to feel the hair growing back within hours of shaving.
This is especially evident in men who develop a five o'clock shadow after having shaved their faces.
This new growth is called stubble.
Stubble typically appears to grow back thicker because the shaved hairs are blunted instead of tapered off at the end, although the hair never actually grows back thicker.
Waxing involves using a sticky wax and strip of paper or cloth to pull hair from the root.
Waxing is the ideal hair removal technique to keep an area hair-free for long periods of time.
It can take three to five weeks for waxed hair to begin to resurface again.
Hair in areas that have been waxed consistently is known to grow back finer and thinner, especially compared to hair that has been shaved with a razor.
Main article: Laser hair removal
Laser hair removal is a cosmetic method where a small laser beam pulses selective heat on dark target matter in the area that causes hair growth without harming the skin tissue.
This process is repeated several times over the course of many months to a couple of years with hair regrowing less frequently until it finally stops; this is used as a more permanent solution to waxing or shaving.
Laser removal is practiced in many clinics along with many at-home products.
Cutting and trimming
See also: Ponytail
People with longer hair will most often use scissors to cut their hair, whereas shorter hair is maintained using a trimmer.
Depending on the desired length and overall health of the hair, periods without cutting or trimming the hair can vary.
Cut hair may be used in wigs.
Global imports of hair in 2010 was worth $US 1.24 billion.
See also: Hairstyle
Hair has great social significance for human beings.
The highly visible differences between male and female body and facial hair are a notable secondary sex characteristic.
She has been growing her hair since 1973, from the age of 13.
Indication of status
Healthy hair indicates health and youth (important in evolutionary biology).
Hair color and texture can be a sign of ethnic ancestry.
White hair is a sign of age or genetics, which may be concealed with hair dye (not easily for some), although many prefer to assume it (especially if it is a poliosis characteristic of the person since childhood).
Although drugs and medical procedures exist for the treatment of baldness, many balding men simply shave their heads.
In early modern China, the queue was a male hairstyle worn by the Manchus from central Manchuria and the Han Chinese during the Qing dynasty; hair on the front of the head was shaved off above the temples every ten days, mimicking male-pattern baldness, and the rest of the hair braided into a long pigtail.
Hairstyle may be an indicator of group membership.
This led to the Parliamentary faction being nicknamed Roundheads.
Recent isotopic analysis of hair is helping to shed further light on sociocultural interaction, giving information on food procurement and consumption in the 19th century.
Female art students known as the "cropheads" also adopted the style, notably at the Slade School in London, England.
Regional variations in hirsutism cause practices regarding hair on the arms and legs to differ.
Some religious groups may follow certain rules regarding hair as part of religious observance.
The rules often differ for men and women.
Many subcultures have hairstyles which may indicate an unofficial membership.
By contrast, among some Indian holy men, the hair is worn extremely long.
In the time of Confucius (5th century BCE), the Chinese grew out their hair and often tied it, as a symbol of filial piety.
Regular hairdressing in some cultures is considered a sign of wealth or status.
In some cultures, having one's hair cut can symbolize a liberation from one's past, usually after a trying time in one's life.
Cutting the hair also may be a sign of mourning.
Tightly coiled hair in its natural state may be worn in an Afro.
This hairstyle was once worn among African Americans as a symbol of racial pride.
Given that the coiled texture is the natural state of some African Americans' hair, or perceived as being more "African", this simple style is now often seen as a sign of self-acceptance and an affirmation that the beauty norms of the (eurocentric) dominant culture are not absolute.
It is important to note that African Americans as a whole have a variety of hair textures, as they are not an ethnically homogeneous group, but an ad-hoc of different racial admixtures.
The film Easy Rider (1969) includes the assumption that the two main characters could have their long hairs forcibly shaved with a rusty razor when jailed, symbolizing the intolerance of some conservative groups toward members of the counterculture.
At the conclusion of the Oz obscenity trials in the UK in 1971, the defendants had their heads shaved by the police, causing public outcry.
During the appeal trial, they appeared in the dock wearing wigs.
Russian Orthodox Church requires all married women to wear headscarves inside the church; this tradition is often extended to all women, regardless of marital status.
Orthodox Judaism also commands the use of scarves and other head coverings for married women for modesty reasons.
Certain Hindu sects also wear head scarves for religious reasons.
Sikhs have an obligation not to cut hair (a Sikh cutting hair becomes 'apostate' which means fallen from religion) and men keep it tied in a bun on the head, which is then covered appropriately using a turban.
Multiple religions, both ancient and contemporary, require or advise one to allow their hair to become dreadlocks, though people also wear them for fashion.
For men, Islam, Orthodox Judaism, Orthodox Christianity, Roman Catholicism, and other religious groups have at various times recommended or required the covering of the head and sections of the hair of men, and some have dictates relating to the cutting of men's facial and head hair.
Some Christian sects throughout history and up to modern times have also religiously proscribed the cutting of women's hair.
Credits to the contents of this page go to the authors of the corresponding Wikipedia page: en.wikipedia.org/wiki/Hair.