Regrowing hairs are new (i.e., recovered) hairs that are growing out of the skin. They're usually spotted on phototrichogram examinations and can be used as an early indication that a treatment might be working.
Regrowing hairs (i.e., upright hairs) appear as follows:
- Thinner at the tip, thicker toward the root. This is because when a hair follicle is forming and just beginning the produce a hair strand, that growth starts as thinner, then progressively transitions to thicker until it reaches its normal hair diameter (where it remains throughout the rest of its hair cycle).
- Pigmented, rather than white and/or wispy. Pigment suggests melanin is being produced at the hair follicle base.
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Upright and/or pointing straight out of the scalp. This is an indication that the new hair growth is strong enough to sustain its weight, and thus is likely not a vellus hair.
Check out this photo for an example (from Dr. Donovan):
