Alopecia means hair loss or baldness. Hair loss occurs for many reasons, from pulling hair out to having it killed off by cancer chemotherapy. Some causes are considered natural, while others signal health problems. Some conditions are confined to the scalp. Others reflect disease throughout the body.

Often conditions affecting the skin of the scalp result in hair loss. The first clue to the specific cause is the pattern of hair loss, whether it be complete baldness, thinning, or patchy bald spots. Another factor is the condition of the hair and the scalp beneath it. Sometimes only the hair is affected, while sometimes the skin is diseased as well.

Male pattern baldness is considered normal in adult men. Hair loss occurs across the top and front of the head, while the scalp remains healthy. Fungal infections of the scalp usually cause patchy hair loss. The fungus, similar to...