The porosity of hair fibers can be modified by chemical and physical damage, influencing their response to cosmetic treatments. To investigate the effect of commonly applied hair care protocols on textured hair, virgin and once-bleached tresses were subjected to multiple cycles of washing, blow-drying while combing, and styling with a hot flat iron, simulating a consumer routine spanning one to six months.

Porosity-related properties were evaluated using swelling test, fluorescence, atomic force, and scanning electron microscopies, high-pressure differential scanning calorimetry, and tensile testing. Both chemical and physical processes induced significant changes in the hair’s water permeability, surface topography, and appearance, alongside a reduction in mechanical and thermal properties, indicating substantial structural alterations compared to virgin hair. Increased porosity compared to virgin hair possibly reduced the heat conductivity of bleached hair, leading to less pronounced effects of heat exposure.

These findings underscore the damaging potential of routine practices for textured hair and emphasize the need for targeted cosmetic solutions to protect and repair these fibers as part of consumers’ hair care regimens.