Hair loss in systemic disease.

A careful history and examination of shed hairs will reveal the etiology of most alopecias due to systemic processes. Telogen effluvium is preceded by a severe systemic stress occurring at least two months prior to the loss of normal club hairs. Most other causes of hair loss involve damage to the hair follicle, which leads to the shedding of dystrophic, brittle anagen hairs. A history of drug ingestion or nutritional compromise or concurrent symptoms suggestive of a genetic, endocrinologic, collagen vascular, or infectious etiology will lead to an accurate diagnosis.