Structural changes of hair shaft after application of chemical hair straighteners: Clinical and histopathological study

Summary Background Chemical hair straightening becomes popular for managing frizzy hair. Keratin in hair care products can penetrate the cortex of the hair fiber improving the mechanical properties of damaged fibers and promote a surface coating that prevents or decreases water diffusion through the hair fibers. This may have beneficial effects on the hair structure; however, the side effects and safety of this treatment have not yet been completely evaluated. Aims To evaluate the efficacy and safety of chemical hair straightening application on the hair shaft. Subjects and Methods Thirty female subjects older than 15 years with hair curl types III–V were included. They were subjected to full history taking and dermatologic examination of hair and scalp prior to and after application of chemical hair straightener. To detect the presence of transverse fissures, split ends, or possible side effects, the distal 3‐5 cm of hair fibers were cut before and after the last step of chemical hair straightener application for light microscopy examination. Three randomly selected samples were examined by transmission electron microscope. Results Chemical hair straightening led to significant decrease in the degree of hair curl and increased hair smoothness and shine. The treated hair fibers showed significant repair of the broken cuticle (P