<p>Postmortem interval (PMI) estimation is a challenging task in forensic investigations. PMI assessment frequently requires the application of the currently available methods which can lead to unsatisfactory results due to the poor accuracy of time interval estimation. To address these concerns, the present study aimed to evaluate whether there is a correlation between human hair proteolysis and PMI. Scalp hair samples of three living donors and eleven individuals exhumed from different burial types from Portuguese cemeteries were analysed by ATR-FTIR (attenuated total reflectance – Fourier-transform infrared). Four band areas and three hair degradation indices were considered in the 2000–1000&#xa0;cm⁻¹ spectral region. When analysing the entire dataset (i.e., 126 infrared spectra) – and when separating and analysing the spectroscopic data by burial type – the ratio between amide II (∼1550&#xa0;cm⁻¹) and S = O and SO₃ combined (∼1074&#xa0;cm⁻¹ and ∼1043&#xa0;cm⁻¹, respectively) suggests there is a correlation between hair proteolysis and PMI (<i>p</i> &lt; 0.05). Nevertheless, it is recommended that a larger dataset is required to confirm the preliminary results obtained in this study and to explore how this correlation can be used to estimate PMI in forensic casework.</p>