The layer that houses the side bonds which determine curl and wave is?

• A. Cortex
• B. Cuticle
• C. Medulla
• D. Epithelium

Answer: (A)

Curl and wave come from the bonds that hold the hair’s keratin fibers together inside the cortex. The cortex is where the side bonds—hydrogen bonds, salt bonds, and especially disulfide bonds—live and determine the shape and elasticity of the hair. Chemical services work by breaking and reforming these bonds in the cortex to create or set a curl. The outer layer, the cuticle, protects the cortex and doesn’t determine curl; the medulla is the central core present in some hairs and isn’t responsible for curl; epithelium isn’t a hair layer involved in shaping curl. So the layer that houses the side bonds determining curl and wave is the cortex.