Vellus hairis short, thin, light-colored, and barely noticeablehairthat 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 externalgenitalareas, thenavel,andscartissue. The density of hair – the number ofhair folliclesperareaof skin – varies from person to person. Each strand of vellus hair is usually less than 2mm(1/13 inch) long and thefollicleis not connected to asebaceous gland.[1]
| Vellus hair | |
|---|---|
 Vellus hair | |
 Comparison of the vellus hair (left) to theterminal hair(right) in humans. | |
| Anatomical terminology |
Vellus hair is most easily observed on children and adult women, who generally have lessterminal hairto obscure it. Vellus hair is notlanugohair. Lanugo hair is a much thicker type of hair that normally grows only onfetuses.
Vellus hair is differentiated from the more visibleterminalorandrogenic hair,which develops only during and afterpuberty,usually to a greater extent on men than it does on women.
TheLatin languageuses the wordvellusto designate "a fleece" or "wool." Vellus hair is sometimes colloquially referred to aspeach fuzz,due to its resemblance to thedownyepidermic growths on thepeachfruit.
Development
editVellus 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,androgenhormones 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 men, this change in vellus hair also occurs on the face (beard) and the body.
Function
editVellus hair provides boththermal insulationand cooling for the body. This insulation regulates body temperature: the vellus hair functions like awickfor 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.
Clinical significance
editOvergrowth
editThe 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 thecortisolhormone in a person withCushing's syndrome.Anorexia nervosaincreases vellus hair. Vellus hair can also be found in men withmale pattern baldnessor 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]
Undergrowth
editThe following conditions may affect growth of the vellus hairs:
- Perioral dermatitis– the hairs may be completely absent in affectedfacialareas.[7]
References
edit- ^Marks, James G; Miller, Jeffery (2006).Lookingbill and Marks' Principles of Dermatology(4th ed.). Elsevier Inc. p. 11.ISBN1-4160-3185-5.
- ^Heather Brannon."Vellus Hair - Peach Fuzz & Puberty Hair Growth".About.com.
- ^ Godfrey, Sheila (2001).The Principle and Practice of Electrical Epilation(3rd ed.). Butterworth-Heinemann.ISBN0-7506-5226-8.
- ^Gündüz, Özge; Aytekin, Asli (1 January 2012)."Trichostasis Spinulosa Confirmed by Standard Skin Surface Biopsy".International Journal of Trichology.4(4): 273–4.doi:10.4103/0974-7753.111201.PMC3681110.PMID23766613.
- ^Lacarrubba, F; Micali, G; Tosti, A (Mar 18, 2013). "Absence Of Vellus Hair In The Hairline: A Videodermatoscopic Feature Of Frontal Fibrosing Alopecia".The British Journal of Dermatology.169(2): 473–4.doi:10.1111/bjd.12316.PMID23496000.S2CID9044042.
- ^Patel, U; Terushkin, V; Fischer, M; Kamino, H; Patel, R (Dec 15, 2012). "Eruptive vellus hair cysts".Dermatology Online Journal.18(12): 7.doi:10.5070/D30DZ2B51S.PMID23286797.
- ^"Perioral dermatitis - Altmeyers Encyclopedia - Department Dermatology".www.altmeyers.org.2020-10-29.Retrieved2021-03-19.