hair
Last reviewed 01/2018
Hair is an keratinized, epidermal, thread-like appendage which grows down into the dermis. It is found on most skin surfaces except:
- palmar surface of hand
- plantar surface of feet
- lips
- urogenital orofices
- penis
In Man, hair has a role as a secondary sexual characteristic under the control of sex hormones e.g. in males, growth of facial terminal hairs at time of puberty and regression of hairline with age. The heat-insulating role of fur in lower animals has been lost in Man.
There are three types of hair:
- lanugo: fetal hair
- vellus: replace lanugo hairs in the peripartum period, unmedullated
- terminal hairs: long, coarse, medullated; typified by scalp and pubic regions
Further, the amount and form of hair varies between races e.g. straight hair in Asians, relatively greater density of hair in those of Mediterranean extraction.