The commonest type of hair loss is male pattern alopecia which is common in both sexes.
Alopecia areata is most commonly seen as well defined round patches of hair loss on the scalp. It may very occasionally become generalised.
A condition called Telogen Effluvium happens when the hair cycle is disturbed causing an increase in the number of hairs that are in the falling out phase to be produced. This typically occurs after childbirth ,certain infectious, surgery or other stressful events. It usually resolves spontaneously.
Scarring alopecias are a collection of conditions usually seen on the scalp that cause destruction of the hair follicle producing scarring resulting in permanent hair loss .examples are Lichen plano pilaris or Discoid lupus.