Hair loss, also known as alopecia or baldness, is a loss of hair from the head or body. Baldness can refer to general hair loss or male pattern hair loss. Some types of hair loss can be caused by alopecia areata, an autoimmune disorder. The extreme forms of alopecia areata are alopecia totalis, which involves the loss of all head hair, and alopecia universalis, which involves the loss of all hair from the head and the body.
Hair loss and hypotrichosis can have many causes, including fungal infection, traumatic damage, such as by compulsive pulling (trichotillomania), as a result of radiotherapy or chemotherapy, and as a result of nutritional deficiencies such as iron deficiency.