Hair is a fibrous protein that grows from follicles found in the dermis, or skin. It is a defining characteristic of mammals, and serves many purposes including protection, regulation of body temperature, and social signaling. Hair is made up of keratin and is composed of dead skin cells. The growth and characteristics of hair, such as color, texture, and length, are influenced by genetics, hormones, and environmental factors. Hair is typically longer and thicker on the head, but can also grow on other parts of the body, such as the eyebrows, eyelashes, and pubic area. Some people choose to style or alter their hair in various ways, such as cutting, coloring, straightening, or curling it. Hair care involves maintaining the cleanliness, health, and appearance of the hair.