Determination of the Cuticle Thickness of Human and Porcine Hairs and Their Potential Influence on the Penetration of Nanoparticles into the Hair Follicles

The study analyzed the hair surface structure of human and porcine hairs using electron microscopy to understand the penetration of nanoparticles into hair follicles. It was found that particles sized 300-600 nm penetrated more efficiently into hair follicles, with the cuticula thickness corresponding to the optimal nanoparticle size for penetration. Human vellus and terminal hairs had a similar cuticula thickness of approximately 530 nm, while porcine ear bristles had a slightly thinner cuticula of approximately 320 nm. This suggested that the cuticula thickness played a role in the efficient penetration and long-term storage of topically applied substances in hair follicles.