How PM2.5 enters and damages skin
Particles below 2.5 microns penetrate the skin's outer lipid layer via transcutaneous absorption. Once inside the stratum corneum, they generate reactive oxygen species (ROS), deplete endogenous antioxidants (vitamin E, CoQ10, glutathione), and activate aryl hydrocarbon receptor (AhR) signalling — the same pathway that causes pollution-induced pigmentation distinct from UV-induced melanogenesis.