Vellus hairs are hairs that do not contain pigment, and do not grow long enough or wide enough to produce cosmetic differences in hair quality. Specifically, vellus hairs:
- May not contain pigment
- Are ≤ 40µm in diameter
- Are ≤30mm in length
In androgenic alopecia, terminal hairs miniaturize over a number of hair cycles until they become vellus hairs. Here is an example of terminal, miniaturizing, and vellus hairs provided by Dr. Donovan:
