What to Know About Vellus Hair

Vellus hair, also referred to as peach fuzz, is the fine, thin, light-colored hair that covers the majority of the body, including the face, arms, stomach, and legs. Vellus hair also tends to be very short and is usually no longer than 2 millimeters. In Latin, vellus means "fleece" or "wool."

One of the primary functions of vellus hair is body temperature regulation, particularly during cold weather. Vellus hair is instrumental in perspiration. When a hair follicle is open, sweat coats the vellus hair and then evaporates, wicking away the sweat. Vellus hair also acts as a sensory function of the skin by alerting you if there's an insect crawling on your arm and registering the sensation of goosebumps.

Hair Follicles

The only parts of the body that don't contain hair follicles are the palms of the hands, the soles of the feet, behind the ears, the forehead, eyelids, nose, lips, the bellybutton, some parts of the genitals and scar tissue.

Hair follicles exist within the dermis—the second layer of skin—and they house stem cells, blood vessels, sebaceous glands, and hair. Vellus hair follicles, however, are not connected to sebaceous glands and therefore do not produce sebum or oil. The hair within the follicle is the living part of the hair. The hair you can see is actually dead.

The majority of hair on the human body is vellus hair. Vellus hair is the hair that exists and grows during childhood, unlike terminal hair, which is influenced by hormones and appears during puberty.

How Puberty Affects Hair Growth

Hair growth is one of the many changes that occurs during puberty. Increased hormone production—androgens, in particular—cause vellus hair to turn to terminal hair on certain parts of the body, including the armpits and pubic area. The vellus hair, which was once smooth and light, becomes coarser, darker and longer. The increase in androgens also causes hairs to develop subcutaneous glands that lubricate hair with oil, which is why puberty and acne go hand in hand.

Females tend to retain more vellus hair than males. Increased hormone production during pregnancy can turn vellus hair into terminal hair, although that hair usually sheds once the baby is born and the female's hormone levels are back to normal. For males, terminal hair grows at a greater rate on more parts of the body, including the face, chest, back, legs, arms, hands, and feet.

Vellus Hair Conditions

Sometimes vellus hair growth is abnormal and can be a sign of disease. For example, increased vellus hair growth can be attributed to an abundance of adrenal hormones in the bloodstream, a condition known as Cushing's syndrome. Anorexia nervosa may also increase the production of vellus hair. The hormonal influence of androgens on hair follicles in conditions of male pattern baldness results in a reversion of scalp hair from terminal to vellus hair.