Most popular theory of alopecia areata states it as an autoimmune disease where the immune system of the body attacks the hair follicles. Inadequate calories and insufficient protein intake will affect your hair, if you are on a crash diet to loose your extra weight. Hair loss can occur. In anorexia nervosa, a psychosomatic problem associated with refusal to eat an adequate amount of food may also affect hair. Severe psychic stress results in sudden loss of hair.
Biological stress is a more common cause of sudden hair loss.
Any number of surgical operations, haemorrhage or shock associated with an accident can cause it. There are number of mechanical stresses on the scalp and hair that can cause hair loss. Post partum alopecia - About two to five months after having a baby, women may suddenly start loosing hair. The hair loss may continue for several months, but eventually there is a complete restoration of normal hair. The cause is not clear.