Beauty Biology: What is hair made of?

Hair is primarily made of a special type of protein called "keratin." Keratin is the same tough, water insoluble material that fingernails and animal horns and hooves are made of. Hair also contains natural oils (lipids) and water. These hair "ingredients" are arranged in 3 primary structures: the cuticle (which is the outermost, shingle-like layer); the cortex (the inside of the hair consisting of bundles of protein filaments; and the medula (a soft spongy-like core in the center of the cortex.)