**Core Concept**
Alopecia areata is an autoimmune disease characterized by a loss of hair on the scalp or other areas of the body. The condition occurs when the immune system mistakenly attacks the hair follicles, leading to hair loss.

**Why the Correct Answer is Right**
Alopecia areata is caused by an autoimmune response against the hair follicles, resulting in the destruction of hair-producing cells and the subsequent loss of hair. The condition often presents with one or more round, smooth patches of hair loss on the scalp. The exact mechanism of the autoimmune response is not fully understood, but it is believed to involve a combination of genetic and environmental factors.

**Why Each Wrong Option is Incorrect**
* **Option A:** Alopecia areata is not caused by a fungal infection, such as ringworm, which is a common cause of hair loss.
* **Option B:** Alopecia areata is not a result of excessive dihydrotestosterone (DHT), which is a hormone that contributes to androgenetic alopecia (male pattern baldness).
* **Option C:** Alopecia areata is not a condition that is typically treated with topical minoxidil (Rogaine), which is a medication used to promote hair growth in cases of androgenetic alopecia.

**Clinical Pearl / High-Yield Fact**
Alopecia areata often presents with a characteristic "exclamation point" sign, where broken-off hairs are seen at the edge of the affected area, with a narrower diameter than the rest of the hair shaft.

**Correct Answer: C. Autoimmune disease.**