The cortex also holds the key to the colour of your hair and contains four pigments - black, brown, yellow and red. The medulla, which is the innermost layer, comprises a core of soft keratin cells. Hair Growth A hair grows upward from the root. Lengthening fibers of keratin-filled dead cells, grouped around the semihollow medulla, which makes up the cortex. Hair grows fastest when it is short.
All mammals have hair, a slender, threadlike outgrowth of the epidermis.
Each strand of hair is composed of a scleroprotein called keratin and lacks both blood vessels and nerves. Both the colour and form of human hair and the shape of the hair follicle serve as reliable determinants of racial and ethnic heredity. It works by protecting polyunsaturated fats, such as linoleic acid from the free radicals, which can be activated by ultra violet light, pollution, and toxins including cigarette smoke and alcohol. F. It plays a vital role in the cell membranes, keeping them flexible and watertight. Lack of vitamin F results in dry, rough, itchy skin.