A sac from which a hair grows and into which the sebaceous (oil) glands open. The follicle is lined by cells derived from the epidermal (outside) layer of the skin.
Each follicle normally goes through a five-year cycle of growth and rest, with about 90% of the follicles growing hair at any one time, averaging about six inches (15 cm) of growth per year. Derived from the Latin word follis, for bag.
“The human hair follicle is a dynamic structure that generates hair through a complex and exquisitely regulated cycle of growth and remodelling governed by numerous genes,” Siobh�n A. Jordan has noted in Molecular Medicine Today.
- Hair loss
Hair loss is the thinning of hair on the scalp. The medical term for hair loss is alopecia. Alopecia can be temporary or permanent. The most common form of hair loss occurs gradually and is referred to as “androgenetic alopecia,” meaning that a combination of hormones (androgens are male hormones) and heredity (genetics) is needed […]
- Hair of the dog
An alcoholic chaser reputed to relieve a hangover, usually needed the morning after imbibing too much alcohol. There is no scientific evidence as to the efficacy of this time-honored treatment for a hangover. The saying originated in the belief that a cure for hydrophobia (rabies) or any disease contracted from a dog bite consisted of […]
- Hair, exclamation point
See Exclamation point hair.
- Hair, lanugal
The downy hair on the body of the fetus and newborn baby. The lanugal hair (or lanugo) is the first hair to be produced by the fetal hair follicles. It is very fine, soft and usually is unpigmented. The lanugal hair is prenatal hair. It appears at about 5 months of gestation and begins to […]
- Hair-on-end skull
Thin fine linear extensions radiating out from the skull that look on an X-ray like hair standing “on-end” from the skull, an appearance associated with hemolytic anemias such as sickle cell disease and thalassemia. The “hair” represents the accentuated trabeculae extending between the inner and outer skull tables through the diploe in the expanded bone […]