The presence of hair is a major differentiator of mammals as a unique class of organisms. It has a sensory function, protects from cold and ultraviolet radiation, and can have a significant psychological impact when its growth or structure is disturbed. In humans it is a highly visible indicator of health status. Hair loss is a common problem that can be improved with vitamin and mineral supplements, as both vitamins and minerals are important for normal cell growth and function and deficiency can contribute to hair loss.