A child presents with a clearly demarcated, round patch of hair loss without any signs of inflammation. What is the most likely diagnosis?

Alopecia areata is characterized by the sudden onset of clearly demarcated, round patches of hair loss that occur without inflammation. In children, this condition is often seen as a well-defined, circular area where hair has fallen out, leaving smooth, hairless skin. The lack of inflammation distinguishes this condition from others, which may present with additional symptoms like redness or itching.

In the case of alopecia areata, the hair loss occurs due to an autoimmune reaction, where the body’s immune system mistakenly attacks the hair follicles. This leads to hair loss that can happen at any time and can even progress to total baldness in some cases, but the defining feature is that the skin appears normal without signs of inflammation.

Other conditions such as scarring alopecia would typically show signs of scarring or changes in skin texture, while tinea capitis often presents with additional symptoms like scalp itching, flaking, or redness due to a fungal infection. Traction alopecia would result from prolonged tension on the hair, commonly seen with certain hairstyles, and would not present as a smooth patch of hair loss. Hence, the presentation described aligns most closely with alopecia areata, making it the most likely diagnosis.