Unintended VOC emissions from cotton and viscose pads complicate olfactory experiments.

The release of volatile organic compounds (VOCs) from sweat pads is modulated by both material composition and conditions of use, particularly moisture content and thermal treatment. In this study, we investigated the impact of water addition and heat exposure on VOC emissions from cotton and viscose–polyester unsampled sweat collection pads using dynamic headspace sampling coupled with two-dimensional gas chromatography–high-resolution time-of-flight mass spectrometry (DHS-GC×GC-Q-TOF-MS). Water addition led to a pronounced increase in VOC release – including key VOCs with low ppbv odor thresholds like acetic acid, 2,4-nonadienal and 2,3-butanedione – with at least a five-fold increase observed for 110 compounds extracted from cotton pads at ambient temperature. Extraction at elevated temperature (60 °C) resulted in even higher fold changes in VOC release. Heat treatment at 150 °C prior to water dosing further amplified VOC emissions. These observations suggest that cellulose–water interactions play a fundamental role in mediating VOC emission dynamics. Our findings highlight the material- and condition-dependent variability in VOC release from sweat collection pads and underscore the need for rigorous control of hydration and thermal effects in chemical and psychophysical studies involving olfactory stimuli. Given the widespread use of cotton pads in psychological and chemosensory research, these methodological considerations are critical for ensuring reliable chemical analysis and reproducible perceptual outcomes. However, these findings do not invalidate previous work, but rather suggest that it should be interpreted with greater caution. The pad technique may still be useful–provided that large sample sizes and appropriate controls are employed–but it is associated with increased noise.