Vellus hair definition - What is vellus hair?

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What is vellus hair?

Vellus hair, colloquially also known as 'peach fuzz', is fine and short strand growing on the body right from childhood. Vellus strands, lacking melanin, are usually unpigmented, light-colored and nearly transparent.

Peach fuzz typically refers to the light colored short hair found on the upper lip of young preadolescent boys. Three types of hairs are present in the human body, namely lanugo, vellus and terminal types. The soft strands can be clearly distinguished from terminal type, which is darker, thicker and longer. It can also be distinguished from lanugo type found on fetus. The lanugo is thicker and longer. The fetus sheds lanugo at 30-36 weeks to be replaced by vellus type. In premature babies lanugo may be seen at birth.

The number of vellus follicles and their distribution in the body are predetermined genetically. Its transformation into terminal type is governed by the gender of the individual, puberty and androgen hormones input. During puberty increase in androgenic hormones cause them to convert into terminal ones in the axillary and pubic areas. During the transition to terminal type, intermediate type of strands can be seen. The soft, light strand's length usually does not exceed 2 mm. due to very short anagen phase.

Vellus hair

Vellus follicles, unlike the terminal follicles, do not connect to sebaceous glands. In children, excluding scalp, eyebrows and eyelashes, the body hair is predominantly soft and short. Vellus is very much apparent is children and women. In men they get reduced due to their transformation into terminal ones, whose presence also obscures the presence of those remaining strands. The vellus strands have many functions such as, body insulation, temperature regulation by aiding sweat evaporation and aiding in the perception of touch sensation.

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Web definition of vellus hair

Definition by thefreedictionary.com: "Short, fine, usually nonpigmented which covers much of the body."

Definition by yourdictionary.com: "Short, fine, light-colored, and barely noticeable hair that develops on most of a person's body from his/her childhood."

Definition by collinsdictionary.com: "short fine unpigmented hair covering the human body."

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Medical conditions involving vellus hair

Accelerated vellus syndrome means a condition wherein the anagen phase of the soft, short strands is extended and accelerated. In this accelerated syndrome the slender light colored downy strands gain length. Accelerated syndrome may occur due certain medications as well as abnormal hormonal activity in postmenopausal women and transgender patients.

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In women with polycystic ovarian syndrome, accelerated syndrome may appear which subsequently convert them into terminal types. This accelerated syndrome is also seen with abundance of vellus as a side effect of diseases like Cushing's syndrome and anorexia nervosa. In male pattern baldness, the bald area is not hairless. The growth of thick, dark terminal strands slow down and the light-colored short vellus strands takeover and cover the bald area.

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Reference:
1.Lacarrubba F, Micali G, Tosti A. Absence of vellus in the hairline: a videodermatoscopic feature of frontal fibrosing alopecia. Br J Dermatol. 2013 Aug;169(2):473-4. doi: 10.1111/bjd.12316.
2.Vogt A, Hadam S, Heiderhoff M, Audring H, Lademann J, Sterry W, Blume-Peytavi U. Morphometry of human terminal and vellus follicles. Exp Dermatol. 2007 Nov;16(11):946-50.

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