## 3 Results and Discussion
### Investigating the Modulation of Skin Volatile Profiles after Fragrance Application
Further reduction (\(p\leq 0.01\)) in fragrance components occurred after 2 h, as observed for phenylethyl alcohol, \(\alpha\)-citral, \(\gamma\)-decalactone, methyl dihydrojasmonate, and 2-ethylhexyl1-4-methoxy cinnamate, accompanied by a reduction (\(p\leq 0.05\)) in linalool acetate, isosafrole, \(\alpha\)-ionone, and dihydro-\(\beta\)-ionone. A number of compounds exhibited a certain degree of temporal stability in skin volatile profiles, including hexanal, undecanal, geranyl acetone, galaxolide, and squalane, where no statistically significant differences were observed within the group as time after fragrance application elapsed. Figure 2: Box plot showing the inter-participant variance for fragrance-derived and endogenous volatiles recovered from participants’ skin headspace at 0 h (red), 1 h (blue), and 2 h (yellow). Box shows middle 50% of data with lines indicating the median. Whiskers represent range within 1.5 IQR. (\(\circ\) represents outliers; \({}^{+}\) indicates compound present in baseline skin volatile samples; \({}^{-}\) indicates that the compound is fragrance-derived). Inter-participant diversity was considered in terms of olfactory qualities. Fragrance-derived compounds were classified according to their olfactory family. The 10 olfactory groups identified consisted of floral, woody, herbal, citrus, musk, fruity, spicy, green, earthy, and terpenic groups. Figure S12 shows the percentage contribution of each olfactory family to individual scent profiles at the times investigated based on peak areas obtained by HS-SPME GC-MS. Floral odours were dominant within scent profiles, where compounds such as methyl dihydrojasmonate and \(\beta\)-linalool were the main contributors. At 0 h, the predominant floral compounds were accompanied by a secondary herbal note attributed to the presence of \(\alpha\)-pinene, \(\beta\)-pinene, and linalool acetate, in addition to a discernible citrus component (limonene, \(\alpha\)-citral, and \(\beta\)-citral). There were minor contributions from all other constituents. After 1 h had elapsed, the predominant floral compounds were accompanied by a diversified composition, with the emergence of musk (galaxolide, 5-cyclohexadecen-1-one), fruity and citrus scents, while herbal and terpenic notes were diminished. After 2 h, the floral note was primarily accompanied by musk and citrus, and there were distinct differences evident between participants' scent profiles (Figure S12). Inter-participant diversity was investigated through comparison of Spearman correlation coefficients for data shown in Figure 2. Correlation analysis can be used to investigate the relationship between two or more variables, and Spearman rank correlation is a common nonparametric approach to measure correlation. It has previously shown potential for distinguishing between individuals based on their skin VOC profiles [34]. The analysis was performed on all 8 participants and generated 28 pairs for each time investigated (0, 1, and 2 h). An overall analysis of all samples (84 pairings) resulted in 88% discrimination at the 0.9 correlation threshold. At a correlation threshold of 0.9, participants were distinguished in 64% of cases immediately after the addition of fragrance at 0 h. This increased to 100% discrimination between participants after 1 and 2 h had elapsed from time of perfume application, thus supporting the presence of diverse scent profiles among participants.