Alopecia is a medical condition that causes hair loss, mostly in small, round patches. There are different types of alopecia, but one of the most common is alopecia areata, which is an autoimmune disease that occurs when the immune system attacks hair follicles. The exact cause of alopecia areata is unknown, but scientists have linked a number of genes to the disease, which suggests that genetics play a role in it. People with certain autoimmune diseases, such as psoriasis, thyroid disease, or vitiligo, are more likely to get alopecia areata, as are those with allergic conditions such as hay fever. Emotional stress or an illness can also bring on alopecia areata in people who are at risk, but in most cases, there is no obvious trigger.

In summary, alopecia is caused by an autoimmune response that attacks hair follicles, and genetics and certain autoimmune diseases or allergic conditions can increase the risk of developing alopecia areata. Emotional stress or an illness can also trigger it in some cases.