Structural Changes of Hair Shaft After Application of Chemical Hair Straighteners: Clinical and Histopathological Study

The study aimed to evaluate the efficacy and safety of chemical hair straightening on the hair shaft. It involved 30 female subjects over 15 years old with hair curl types III–V. The subjects underwent dermatologic examination before and after the application of a chemical hair straightener, and their hair fibers were analyzed using light microscopy and transmission electron microscopy. The results showed that chemical hair straightening significantly decreased hair curl and increased smoothness and shine, with a notable repair of the broken cuticle (P < 0.001). However, there was no significant improvement in transverse fissures or split ends (P = 0.60 and 0.74, respectively). The study concluded that while chemical hair straightening has beneficial effects on the hair shaft, it may also lead to side effects, indicating a need for safer hair straightening methods.