What is Vellus Hair
Vellus hairs are a type of human hair that are fine, short, light-colored or transluscent, and non-pigmented that develop from childhood and are found on most areas of the body. Their growth is not, in contrast to terminal hairs, affected or dictated by hormones. Vellus hair is the technical term for “peach fuzz” which is what it is called in the urban dictionary. Peach fuzz usually refers to the light and sparse hair found on the upper lip of most young boys.
Vellus hairs are usually no longer than two millimeters, and their follicles are not associated with sebaceous glands. The shafts of vellus hairs are roughly the same or smaller than their internal root sheaths while the bulb of the follicle are located at the upper dermal part of the skin.
There is some evidence indicating a connection between the activity of sebaceous glands and the growth of vellus hairs. Since vellus hairs have no underlying sebaceous glands, pre-pubertal children do not develop acne and other skin conditions which are associated with these glands.
Vellus hairs can be more prominent on females and children because they do not have as many terminal hairs as adult males, which tend to obscure vellus hairs.
Types of human hairs
Vellus hairs are one of three types of hairs that are found on humans. The other two are lanugo hairs and the aforementioned terminal hairs. Lanugo hairs are thicker hairs which are also called first hairs, because they only grow on the unborn fetus. The pigmented and long hairs located at the scalp as well as the other body parts are known as terminal hairs.
After forty weeks in gestation, the fetus sheds its lanugo hair, and replaces it with vellus hair. This in turn is also shed in some areas during the pubertal stage to make way for the growth of terminal hairs. Terminal hairs are also called androgenic hairs; men’s bodies have more proliferation of such hairs than women.
Upon reaching puberty, hormones known as androgens are released into the blood circulation, and these transform the vellus hairs in some areas of the body into terminal hairs. These hormones are testosterones in males and become converted into estrogen in females.
Androgens also stimulate hair growth in other areas. Hairs develop subcutaneous glands which lubricate them with oils. This is the reason why acne is rampant during puberty and adolescence. Hairs also grow longer and become thicker and darker. Facial and body hairs are affected in males, and terminal hairs such as those found at the pubic area and armpits start to grow.
Location of Vellus Hairs in the Body
Most body parts have vellus hair growth. Vellus hairs are those fine and small hairs that are found on faces, the back of the toes and fingers, at the chest, and at the back. There are no vellus hair growth at the area behind the ears, at the forehead, eyelids, nose, lips, at the root sections of terminal hairs, navel, soles, on scars, some parts of the external genitalia, and on palms.
The Significance of Vellus Hair
Vellus hairs provide significant body insulating properties, and help the body regulate its temperature. They also serve as a cooling mechanism by being conduits in removing sweat. Vellus hairs function like that of a wick, wherein a drop of sweat that comes out of an open skin pore wets the vellus strand. As the sweat goes through the strand, it starts to evaporate, producing a cooling effect on the skin surface. As more sweat drops come out of the pore, these continuously wet the vellus hairs and evaporate on them. This is basically the process of perspiration. Vellus hairs thus serve an essential function in thermoregulation, despite being seemingly small and unimportant.
Vellus hairs also serve as extensions of the sensory functions of the skin. They register sensations when a creature crawls on the skin as well as when goosebumps are felt.
The abnormal growth and proliferation of vellus hairs are associated with certain physical and mental illnesses. Cushing’s disease, for example, is the abnormal increase of adrenal hormones in the bloodstream, which can result in the overabundance of vellus hair formation. This is also the case in persons with anorexia nervosa, a dietary condition. There are can also be a proliferation of vellus hairs in men with a condition of male baldness, and also in cases of hirsutism.
In fetuses, unusual hormonal fluctuations in the blood of pregnant females can precipitate the development of terminal hair growth from fetal vellus hairs. When the baby is born, these hairs are subsequently shed off due to the resumption of normal hormonal levels in their body.