Dose-Dependent Histopathological and Structural Impact of Chemical Hair-Straighteners on Scalp Epithelium and Hair-Fibres Using Albino Wistar Rats

Dose-dependent Effects of Chemical Hair Straightener on Hair and Scalp

Abstract

Chemical hair straighteners are popular for creating straight, smooth hair but contain strong chemicals such as
formaldehyde, sodium hydroxide, and parabens, which disrupt the keratin structure by breaking disulfide bonds, critical for hair strength and shape. These chemical interactions often lead to hair and scalp damage, including irritation, inflammation, thinning, burns, and follicular injury. Repeated use has been linked to higher risks of hormone-related cancers, which raises important public health questions. This study investigated how dose and frequency of chemical hair straightener application affect scalp skin and hair fibre histopathology in albino Wistar rats. The research utilized controlled single and multiple topical exposures to a commercial straightener product over various durations. Hair samples were analyzed for porosity and microstructural changes using wet preparation microscopy and a modified buoyancy test, while scalp tissue sections were examined via haematoxylin and eosin staining. Findings showed that hair damage intensified with repeated chemical exposure, progressing from initial cortical fading and cuticular lifting to severe keratin degeneration and pigment loss. Histological analysis of scalp samples revealed dose-dependent effects, including epidermal thinning, keratinocyte necrosis, follicular atrophy and disruption of collagen matrix, all of which worsened with prolonged treatment. These findings underline the cytotoxic potential of chemical hair straighteners and risks related to systemic absorption of their chemical ingredients. Although the study’s limitations include the use of an animal model and evaluation of only one product, the results provide a vital basis for further research in humans, chronic toxicity assessment, and development of safer hair cosmetic practices.