It is called alopecia areata. It presents as localized patches of hair loss. Commonly seen on scalp or beard. It can also been seen on other parts of the body.
It is an auto immune condition (in which the body attacks its own hair follicles in the growing phase).
It is seen in association with diabetes, thyroid disorders, rheumatoid arthritis.
Other causes include stress and anxiety.
It is called alopecia areata. It presents as