The health and beauty of human hair have immeasurable psychological importance. Hair structure and its cycle are influenced by intentionally or nonintentionally delivered factors such as grooming, heat styling, chemical agents and climatic exposure. All of these factors are capable of causing loss of hair color and luster, harshness, stiffness, weakness, brittleness and flyaway, transient loss of hair or scarring alopecia. In this review we describe the effects of various exogenous agents on hair, including hair cosmetics, traction, heat, water, solar radiation and X-irradiation.