What type of alopecia features patchy loss of hair on the scalp or body?

Alopecia areata is characterized by sudden, patchy loss of hair, which can occur on the scalp as well as on other parts of the body. This type of hair loss often appears in circular areas and can affect individuals regardless of age or gender. It is thought to be an autoimmune condition, where the body's immune system mistakenly attacks hair follicles, leading to hair loss in specific areas.

This distinct feature of localized, patchy hair loss sets alopecia areata apart from other types of alopecia. For instance, alopecia totalis results in total loss of hair on the scalp, and alopecia universalis leads to complete loss of hair on the entire body. Diffuse alopecia, on the other hand, refers to an overall thinning or shedding of hair rather than localized patches. Therefore, the focus on the patchy nature of hair loss makes alopecia areata the correct answer to this question.