Background: Skin diseases such as seborrheic dermatitis(SD), psoriasis, and atopic dermatitis(AD) are the most common diseases affecting scalp hair. Fourier transform infrared (FT-IR) spectroscopy was used to analyze the chemical properties of the hair shaft. Objectives: In thist study, we investigated the effects of scalp dermatitis(SD, psoriasis, and AD) on the chemical properties of hair keratin using FT-IR spectroscopy. Methods: Hairs were collected from lesional regions affected by SD, psoriasis, and AD and non-lesional regions separately and hairs of 20 normal adults. The FT-IR absorbance bands were analyzed by the Gaussian model to obtain the center frequency, half width, height, and area of each band. Results: The spectra of hair with scalp dermatitis were different with that of control, the amide A components centered at 3278 cm-1 were smaller than those of the control. The psoriasis hair showed a large difference in the IR absorbance band between lesional and non-lesional hairs indicating good agreement with the morphological changes. The hairs with diseases did not show differences in the content of cystine, which was centered at 1054 cm-1, from the control. Conclusion: The chemical properties of keratin were not signi ficantly different between the hairs affected by SD, psoriasis, and AD. However, the changes induced by scalp dermatitis were different with weathering. Therefore, FT-IR analysis could be used to screen differences between the pathological conditions of scalp hair.