Diffuse hair loss can affect both sexes at any age. Anything that interrupts the normal hair cycle can trigger diffuse hair loss. Triggers include a wide variety of physiologic or emotional stresses, nutritional deficiencies, and endocrine imbalances. Loss of telogen-phase hairs is the most common. Hair loss during the anagen phase is usually caused by chemotherapy or radiation therapy. Finding the cause, or trigger, of the hair loss requires a thorough history and examination and will enable appropriate treatment. Patient education is key in the management of diffuse hair loss.