Cuticle

The cuticle is the outermost layer of the hair fiber — overlapping scales of flattened, dead keratinized cells that protect the cortex underneath. Cuticle integrity controls shine, smoothness, and the rate at which water and chemistry penetrate to the cortex.

Background

A healthy cuticle lies flat against the fiber, with scales pointing toward the tips. Light reflects coherently off a flat cuticle, which is what we perceive as shine. A roughened or lifted cuticle scatters light and feels rough.

Damage to the cuticle is mostly mechanical and surface-chemical: friction, heat, and surfactant stripping. Bleach also opens the cuticle to allow the bleach itself to penetrate to the cortex.

The cuticle is the gatekeeper for any treatment that needs to reach the cortex. Reconstruction molecules — including ANATOMY's Pro-amino X and Aminalyl S — must diffuse across the cuticle to reach the cysteine residues where the click-chemistry reactions occur. A cuticle that has been over-coated by silicones or heavy conditioners can resist that diffusion.

What cuticle treatments do well: - Surface smoothing - Light-reflection (shine) - Reducing wet-comb friction

What cuticle treatments do not do: - Restore disulfide bonds inside the cortex - Reverse keratin denaturation - Build new covalent crosslinks

Cuticle and cortex are different problems with different solutions. Most "softer hair" and "shinier hair" claims operate at the cuticle level. Most "stronger hair" and "structural" claims need to operate at the cortex.