Alopecia is a general term that refers to hair loss, but there are specific types of alopecia you may have. Hair loss, also called alopecia, is a disorder caused by an interruption in the body’s cycle of hair production. Hair loss can occur anywhere on the body, but most commonly affects the scalp. On average, the scalp has 100,000 hairs that cycle through periods of growing, resting, falling out, and regenerating.