Hair follicle

Hair follicle
Hair follicle
A photograph of hair on a human arm emerging from follicles
Details
System	Integumentary system
Artery	Supratrochlear, supraorbital, superficial temporal, occipital
Vein	Superficial temporal, posterior auricular, occipital
Nerve	Supratrochlear, supraorbital, greater occipital, lesser occipital
Lymph	Occipital, mastoid
Identifiers
Latin	folliculus pili
MeSH	D018859
TA98	A16.0.00.023
TA2	7064
TH	H3.12.00.3.01034
FMA	70660
Anatomical terminology [edit on Wikidata]

The hair follicle is an organ found in mammalian skin.^[1] 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 hormones, neuropeptides, and immune cells.^[1] This complex interaction induces the hair follicle to produce different types of hair as seen on different parts of the body. For example, terminal hairs grow on the scalp and lanugo hairs are seen covering the bodies of fetuses in the uterus and in some newborn babies.^[1] The process of hair growth occurs in distinct sequential stages: anagen is the active growth phase, catagen is the regression of the hair follicle phase, telogen is the resting stage, exogen is the active shedding of hair phase and kenogen is the phase between the empty hair follicle and the growth of new hair.^[1]

The function of hair in humans has long been a subject of interest and continues to be an important topic in society, developmental biology and medicine. Of all mammals, humans have the longest growth phase of scalp hair compared to hair growth on other parts of the body.^[1] For centuries, humans have ascribed esthetics to scalp hair styling and dressing and it is often used to communicate social or cultural norms in societies. In addition to its role in defining human appearance, scalp hair also provides protection from UV sun rays and is an insulator against extremes of hot and cold temperatures.^[1] Differences in the shape of the scalp hair follicle determine the observed ethnic differences in scalp hair appearance, length and texture.

There are many human diseases in which abnormalities in hair appearance, texture or growth are early signs of local disease of the hair follicle or systemic illness. Well known diseases of the hair follicle include alopecia^[2] or hair loss, hirsutism or excess hair growth and lupus erythematosus.^[3][2]