Vellus hair is the short, fine, and often light-colored hair that covers most of the human body. Think of it as "peach fuzz."
Characteristics of Vellus Hair
Unlike terminal hair, which is the thicker, longer, and pigmented hair found on the scalp, face (in men), armpits, and pubic area, vellus hair has distinct characteristics:
- Thin and Fine: It's considerably thinner in diameter than terminal hair.
- Short: Vellus hair typically grows to a very short length, usually less than 2mm.
- Lightly Pigmented or Colorless: It often lacks pigment, appearing translucent or light blonde.
- Lacks a Medulla: The medulla, the innermost layer of the hair shaft, is usually absent in vellus hair.
- Covers Most of the Body: It is found on areas like the arms, legs, torso, and face (except for areas with terminal hair and areas like the palms of the hands and soles of the feet).
Function of Vellus Hair
While the exact function of vellus hair isn't fully understood, some potential roles include:
- Sensory Perception: Vellus hair follicles are connected to nerve endings, making the skin sensitive to light touch and airflow.
- Thermoregulation: It may provide a small amount of insulation.
- Facilitating Sweat Evaporation: It can help wick sweat away from the skin.
Vellus Hair vs. Terminal Hair
The following table summarizes the key differences between vellus and terminal hair:
| Feature | Vellus Hair | Terminal Hair |
|---|---|---|
| Thickness | Thin | Thick |
| Length | Short | Long |
| Pigmentation | Light or absent | Dark and pigmented |
| Medulla | Usually absent | Present |
| Location | Most of the body | Scalp, face, armpits, pubic area |
| Function | Sensory, Thermoregulation | Protection, Social Signaling |
Transformation of Vellus Hair to Terminal Hair
Under the influence of hormones, particularly androgens, vellus hair can transform into terminal hair. This process is most noticeable during puberty, when vellus hair on the face of males becomes thicker and darker, resulting in facial hair. Similar transformations occur in the armpits and pubic areas of both sexes.
