Comparative FT-IR Spectroscopy Salivary Profiles of University Students: E‑Cigarette Users vs Nonusers

This study investigated whether the use of e-cigarettes induces detectable alterations in salivary composition through Fourier-transform infrared spectroscopy (FT-IR). Saliva samples were collected from 60 young university students (30 e-cigarette users and 30 nonusers) at the University of Taubaté (Taubaté-SP). A total of 181 spectra were acquired in triplicate, resulting in 90 spectra for e-cigarette users and 91 for controls, because one control was measured in quadruplicate. Data were preprocessed by baseline correction, Savitzky-Golay smoothing, and vector normalization. Three spectral regions were examined (3050-2800 cm^-1, 1720-1490 cm^-1, and 1200-900 cm^-1), and discriminatory analysis was performed using a Support Vector Machine (SVM) classifier with repeated 10-fold cross-validation. In the 3050-2800 cm^-1 region, controls exhibited five peaks (3290, 2962, 2925, 2874, and 2853 cm^-1), while e-cigarette users showed six, including a unique band at 3273 cm^-1 and shifts at 3288 and 2851 cm^-1. In the 1720-1490 cm^-1 amide region, controls presented peaks at 1640 and 1546 cm^-1, whereas users exhibited peaks at 1649 and 1544 cm^-1, indicating possible protein alterations. This region yielded the best classification performance (accuracy ∼ 0.65; F1-score ∼ 0.72; AUC ∼ 0.73). In the 1200-900 cm^-1 fingerprint region, both groups shared a coincident peak at 1077 cm^-1 with only minor intensity differences. There was not a clear separation between cigarette user and nonsmokers groups by PCA analysis. Within the limitations of this study, the findings suggest that e-cigarette use may induce measurable biochemical changes in saliva, particularly in protein- and lipid-associated vibrational modes. These alterations could impair salivary defense functions, underscoring the importance of dental professionals in preventive counseling.