What is Alopecia? Alopecia, in its most general definition, is the loss of hair. Many forms of alopecia include temporary hair loss or thinning of the hair and are caused by a number of factors, including diet, trauma to the hair follicles, illness, medications, and so on. The two main types of permanent alopecia are alopecia areata and androgenetic alopecia. With alopecia areata, hair falls out in spots all over the body. This form of alopecia occurs mostly in men and women over the age of 30 but in rare cases may affect children and teenagers. Androgenetic alopecia is what most people commonly call male pattern hair loss or woman diffuse hair loss and occurs only on the head. In men, hair loss occurs gradually beginning at the temples (usually forming an M as the hair line recedes) and crown of the skull. In women, hair becomes thinner around the whole scalp but rarely results in complete baldness.