Light micrograph of a section of human skin, with a single hair. The outer layer of the skin, the epidermis, is the thin, dark brown band, supported by the much deeper but less dense dermis. The dermis merges into the subcutaneous layer at the bottom of the picture. The epidermis grows down to form the lining of the hair shaft or follicle. The hair is rooted in an enlarged "hair bulb", where actively dividing cells make the hair grow. Associated with the follicle is smooth muscle, to pull the hair erect in cold or fear, & one or more sebaceous glands that secrete oily sebum onto the hair & skin surface. A sebaceous gland is seen half way down the left side of this follicle.