Hair generally can be straight, wavy, curly, or kinky. A human hair strand includes three concentric layers known as the cuticle (a thin, outer-most shell), the cortex (the main body of the hair), and the medulla (a thin, central core). The cuticle and cortex provide the hair strand's mechanical properties, that is, its tendency to have a wave, curl, or kink. Condition of the cuticle is responsibl