A vellus hair is a very fine, colorless or light-colored hair that is found on most parts of the human body. Aside from not containing color pigments, vellus hairs are instantly recognizable by their small size; they generally are not more than about 0.08 inches (2 mm) in length, and their shafts are about the same size as or smaller in diameter than their inner root sheaths. The bulb of a vellus hair follicle is found in the upper dermis region of the skin, and the follicle is not connected to a sebaceous gland. Some research, however, appears to indicate a relationship between sebaceous gland activity and vellus hair growth.
Types of Hairs on the Body
Vellus hairs are one of three human hair types, along with lanugo hairs and terminal hairs. Lanugo hairs, also known as the first hairs, are found only on fetuses while they are still in the womb. Terminal hairs are the long, pigmented hairs found on the scalp and other parts of the body. Vellus hair develops after the lanugo hair is shed at about 40 weeks of gestation, and is in turn replaced by terminal hair on some parts of the body during puberty.
Locations of Vellus Hairs
In both sexes, vellus hairs can be found in most parts of the body, with some exceptions. On the head, vellus hairs typically are not found on the lips, the nose, the eyelids, the forehead and the backs of the ears. Other parts of the body where vellus hairs are not usually found include the palms, the soles of the feet, the navel and the terminal hair root sections.
The fine hair that can be seen on the face, on the backs of the fingers and toes and on the trunk is vellus hair. When a person reaches puberty, certain hair-modulating chemicals known as androgens transform vellus hairs into terminal hairs in some areas. Androgens also induce new hair growth in other areas. For instance, there are changes in the vellus facial hair and body hair in males, and armpit hair and pubic hair begin to develop in both males and females.
Purposes of Vellus Hairs
Although people in many cultures, especially women, attempt to remove body hair from certain areas, vellus hairs serve a purpose. They provide insulation to the body, help regulate the body's temperature and serve as conduits for the removal of perspiration. Despite their small size and propensity for going unnoticed, vellus hairs are quite important for a person's general well-being.