Vellus-like hairs are < 0.03 mm in diameter and rarely grow > 1-2 mm.
Terminal hairs are coarse > 0.06 mm in diameter and can grow up to 3 feet. A
true vellus hair does not have an attached arrector pili muscle. Only miniaturized
vellus-like hairs of androgenetic alopecia have arrector pili muscle.