Hair cuticle

The hair cuticle is the outermost protective layer of the hair shaft, composed of multiple layers of overlapping, keratinized cells known as scales (Robbins, C. R., Chemical and Physical Behavior of Human Hair, 2012). Its primary biological function is to serve as a physical and chemical barrier that protects the inner cortex from environmental stressors, UV radiation, and mechanical damage (Vogt et al., Journal of Investigative Dermatology, 2008). The cuticle also regulates the hydration of the hair fiber through a specialized lipid layer, primarily 18-methyleicosanoic acid (18-MEA), which provides hydrophobicity and reduces friction (Masukawa et al., Journal of Cosmetic Science, 2005). While the hair cuticle is not a traditional molecular target for systemic drugs, it is the primary site of action for topical dermatological agents and cosmetic treatments aimed at managing hair shaft disorders like trichorrhexis nodosa (StatPearls, "Hair Pathology", 2023). Damage to the cuticle, often termed weathering, leads to increased porosity and fragility, making its preservation a key goal in hair health and dermatological science.

Other names

Cuticula piliHair scale layerExocuticle

Topical agents interact with the cuticle by coating the scales, restoring the lipid barrier, or adjusting pH to flatten the cuticle scales.