There are many causes of alopecia (hair loss). It can be sudden or gradual. Causes include drug allergies, viral illnesses, auto immune and thyroid disorders plus certain restrictive diets.
Alopecia areata is the commonest autoimmune cause of hair loss which is usually patchy and sudden. Corticosteroid injections into the skin of scalp can help.
New treatments for male and female pattern thinning are now available.