Vellus hair
Vellus hair
Comparison of the vellus hair (left) to theterminal hair (right) in humans.
Anatomical terminology [edit on Wikidata]

Vellus hair is short, thin, light-colored, and barely noticeablehair that develops on most of a human's body duringchildhood. Exceptions include thelips, the back of theear, the palm of thehand, the sole of the foot, some externalgenital areas, thenavel, andscar tissue. The density of hair – the number ofhair follicles perarea of skin – varies from person to person. Each strand of vellus hair is usually less than 2 mm (1⁄13 inch) long and the follicle is not connected to asebaceous gland.^[1]

Vellus hair is most easily observed on children and adult females, who generally have lessterminal hair to obscure it. Vellus hair is notlanugo hair. Lanugo hair is a much thicker type of hair that normally grows only onfetuses.

Vellus hair is differentiated from the more visibleterminal orandrogenic hair, which develops only during and afterpuberty, usually to a greater extent on men than it does on women.

TheLatin language uses the wordvellus to designate "a fleece" or "wool". Vellus hair is sometimes colloquially referred to aspeach fuzz, due to its resemblance to thedowny epidermic growths on thepeach fruit.

Vellus hair replaces lanugo hair on a human fetus at 36 to 40 weeks ofgestation.^[2] The growth cycle of vellus hair is different from the growth cycle of terminal hair. Atpuberty,androgen hormones cause much of the vellus hair to turn into terminal hair and stimulate the growth of new hair in the armpit and thepubic area. In males, this change in vellus hair also occurs on the face (beard) and the body.

Vellus hair provides boththermal insulation and cooling for the body. This insulation regulates body temperature: the vellus hair functions like awick for sweat. While a skin pore is open, sweat wets a strand of vellus hair. The sweat on the external part of the strand evaporates. More sweat wets the external part of the vellus strand and then evaporates. This process is calledperspiration.

The unusual growth of vellus hair can be a side effect of some types of disease. An abundance of vellus hair can develop from an increase in the production of thecortisol hormone in a person withCushing's syndrome.Anorexia nervosa increases vellus hair. Vellus hair can also be found in men withmale pattern baldness or withhirsutism. Hormonal fluctuations in pregnant women cause foetal vellus hair to change to terminal hair. The terminal hair is usually shed after the birth of the baby upon the return of the hormones to the normal levels.^[3]

• Trichostasis spinulosa – Diagnosed by observing lesions due to multiple tufts of vellus hair located in a keratinous sheath.^[4]
• Frontal fibrosing alopecia, a clinical variant oflichen planopilaris, is a female scarring alopecia characterized by progressive recession of the frontotemporal hairline. It is characterised by the absence of vellus hair in the hairline.^[5]
• Eruptive vellus hair cyst (EVHC), a benign dermatologic condition in children and young adults.^[6]

The following conditions may affect growth of the vellus hairs:

• Perioral dermatitis – the hairs may be completely absent in affected facial areas.^[7]

• Hair anatomy

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