Unwanted Hair - Definitions

Anagen

This is the growth stage of the hair follicle. 90% of scalp hair and 80-85% of beard and moustache hair is in anagen at any given time. There is an enzyme called ornithine decarboxylase (ODC) that makes the hair shaft grow. This converts ornithine into putresine which allows hair to continue growing. ODC is only present in anagen hairs. Testosterone increases hair growth except on the scalp.Oestrogen inhibits hair growth making a finer less pigmented hair.

Catagen

This is the involution of the hair follicle.

Telogen

This is the resting phase in the hair follicle. These have club shaped roots. This phase is 2-7 years long in scalp hair, 5-6 months in upper-lip and 1 year in the beard area. This phase lasts 3-4 months on the scalp, 6 weeks on the upper lip and 1 month on the beard area.

Exogen

This is the hair shedding.

Vellus Hair

These are very short, fine hairs that do not have any pigment. They do not have any muscle attached to them. Sometimes these vellus hair follicles can have large oil glands associated with them. They undergo a full hair cycle which is shorter than seen in terminal hair.

Terminal Hair

This is usually large, pigmented, mature hair. These hairs such as in the eyebrows, eyelashes, scalp. Under the influence of testosterone the hairs in the pubis area and armpits start as vellus hair and change to terminal hairs in childhood.

Lanugo Hair

This is very fine hair found on the newborn in the first few weeks of life.

Effluvium

This is excess shedding of hair.

Alopecia

This is abnormal hair loss.