Molecular Characterization of Human Scalp Hair Using ATR-FTIR Spectroscopy: Implications for Hair Health and Biological Assessment

Abstract

Human scalp hair contains keratin proteins, lipids, and other biochemical constituents that may provide useful molecular information for forensic analysis. This study aimed to characterize the spectral profile of human scalp hair using attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy and evaluate spectral similarities and variations among individuals with different demographic characteristics and scalp conditions. Nine hair specimens collected from five males and four females across different age groups and scalp conditions were analysed using a PerkinElmer Spectrum Two FT-IR spectrometer equipped with a diamond ATR crystal. Spectral data were acquired over 4000–400 cm⁻¹ at a resolution of 4 cm⁻¹ using 32 co-added scans, followed by baseline correction, normalization, and ATR correction. The spectra consistently demonstrated characteristic absorption bands corresponding to Amide I (1630–1634 cm⁻¹), Amide II (1513–1537 cm⁻¹), Amide III (1232–1236 cm⁻¹), and lipid-associated CH₂ stretching vibrations (2920–2923 and 2851–2856 cm⁻¹). Comparatively greater spectral variation was observed within the 1200–900 cm⁻¹ fingerprint region, whereas the major spectral features were broadly similar between male and female specimens. The specimen from an individual with androgenetic alopecia retained the principal absorption features observed across the dataset. These preliminary findings suggest that ATR-FTIR spectroscopy may offer a rapid and minimally destructive approach for molecular characterization of human scalp hair. Further studies involving larger cohorts, replicate measurements, and quantitative chemometric analyses are necessary to establish its reproducibility and forensic applicability.