Alopecia areata is a medical condition where hair loss occurs in small well-defined patches. In mild cases, or when the condition is first taking effect, these patches may not be noticeable to others, but they can worsen to the point where you may feel self-conscious about your appearance. Alopecia areata can be variable in its severity and distribution resulting in isolated patchy hair loss, complete hair loss on the scalp, or complete hair loss over your entire body.