Skin. Artwork of a section of human skin. A fully developed hair pierces the epidermis (light brown and pink) at left, at right a hair is growing from its follicle. Halfway down the follicle on the left is a sebaceous gland (yellow), which produces oily sebum, and to the right of the hair is a hair erector muscle. Also seen within the dermis are coiled sweat glands (green), sensory nerves (also green) and blood vessels (red and blue). Fat deposits (yellow) are found in a subcutaneous layer below the dermis. Skin is the first line of defence against infection, and also plays an important role in maintaining a constant body temperature.