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]
^ abcdefBlume-Peytavi, Ulrike (2008). Hair growth and disorders. Berlin: Springer. ISBN 9783540469117. OCLC 272298782.
^ abErjavec SO, Gelfman S, Abdelaziz AR, Lee EY, Monga I, Alkelai A, Ionita-Laza I, Petukhova L, Christiano AM (Feb 2022). "Whole exome sequencing in Alopecia Areata identifies rare variants in KRT82". Nat Commun. 13 (1): 800. Bibcode:2022NatCo..13..800E. doi:10.1038/s41467-022-28343-3. PMC 8831607. PMID 35145093.
^Gilhar, Amos; Etzioni, Amos; Paus, Ralf (2012-04-19). "Alopecia areata". The New England Journal of Medicine. 366 (16): 1515–1525. doi:10.1056/NEJMra1103442. ISSN 1533-4406. PMID 22512484. S2CID 5201399.
The hairfollicle 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...
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...
pilosebaceous unit of the hairfollicle (HF), and irreversible hair loss. Traction alopecia is caused by adding too much strain on the hair on one's head. Tight...
Hair transplantation is a surgical technique that removes hairfollicles from one part of the body, called the 'donor site', to a bald or balding part...
Laser hair removal is the process of hair removal by means of exposure to pulses of laser light that destroy the hairfollicle. It had been performed experimentally...
(SHBG), follicle stimulating hormone (FSH), testosterone, and epitestosterone when compared to men without pattern hair loss. Although hairfollicles were...
a threshold for the proliferation of hairfollicle cells. From childhood onward, regardless of sex, vellus hair covers almost the entire area of the human...
Human hair color is the pigmentation of human hairfollicles and shafts due to two types of melanin: eumelanin and pheomelanin. Generally, the more melanin...
would produce healthy hair. In 2015, initial trials for human hair were successful in generating new follicles, but the hairs grew in various different...
Demodex /ˈdɛmədɛks/ is a genus of tiny mites that live in or near hairfollicles of mammals. Around 65 species of Demodex are known. Two species live on...
in the skin that opens into a hairfollicle to secrete an oily or waxy matter, called sebum, which lubricates the hair and skin of mammals. In humans...
ceases to be produced in the hair root and new hairs grow in without pigment. The stem cells at the base of hairfollicles produce melanocytes, the cells...
for procedure is also recommended. Hair transplantation is a surgical technique that moves individual hairfollicles from a part of the body called the...
for many fight-or-flight responses. The muscle cells connected to the hairfollicle have been visualized by actin immunofluorescence. Arrector pili muscle...
follicle it pushes older cells out and that is what becomes the leg hair. After the older cells become hard and leave the follicle, they form a hair shaft...
the infection and inflammation of one or more hairfollicles. The condition may occur anywhere on hair-covered skin. The rash may appear as pimples that...
destroy the hairfollicle, replace it with scar tissue, and cause permanent hair loss. A variety of distributions are possible. In some cases, hair loss is...
The living parts of hair (hairfollicle, hair root, root sheath and sebaceous gland) are beneath the skin, while the actual hair shaft which emerges (the...
among people who have coarse or curly hair. It may or may not be accompanied by an infection of the hairfollicle (folliculitis) or "razor bumps" (pseudofolliculitis...
more hair growing from the head. The curly quality comes from the shape of the hairfollicle, as straight hair grows from more circular hairfollicles, and...
also known as hair erector muscles, are small muscles attached to hairfollicles in mammals. Contraction of these muscles causes the hairs to stand on end...
skin) is a common, autosomal-dominant, genetic condition of the skin's hairfollicles characterized by the appearance of possibly itchy, small, gooseflesh-like...
hair-thin, solid metal probe into each hairfollicle without puncturing the skin (when inserted properly). Electricity is delivered to the follicle through...
tissue. The density of hair – the number of hairfollicles per area of skin – varies from person to person. Each strand of vellus hair is usually less than...
diseases, particularly at the hairfollicle. Alterations to PAD activity resulted in the development of Uncombable Hair Syndrome. Another study examined...
condition that occurs when dead skin cells and oil from the skin clog hairfollicles. Typical features of the condition include blackheads or whiteheads...
being visible. Pubic hair forms in response to the increasing levels of testosterone in both girls and boys. Those hairfollicles that are located and...
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