## 4 Conclusions  
The present research has shown that in vivo HS-SPME GC-MS analysis is a valuable method to investigate the volatile composition of human odour. Profiling VOCs offers a non-contact method of chemical interrogation that is repeatable and can easily be performed on human participants and is also suitable for use in vivo on skin models. The method permits repeated evaluation of scent profiles during fragrance evaporation on skin. Fifty-one VOCs derived from fragrance and endogenous sources were identified in participants' skin in this study. The information generated was used to assess the diversity across the participant population, where the potential to discriminate between individuals based on Spearman rank correlation was demonstrated, suggesting diverse scent profiles existed amongst participants over time. This study has a number of limitations including the low number of participants and the fact that only reliably identified VOCs were reported, thus a number of potentially notable compounds were not yet considered in the context of this investigation. In future research, it will be important to address regional diversity in skin volatiles (owing to the diverse distribution of glands on human skin), and the contribution of skin flora to volatile emanations and their influence on fragrance evolution. This approach could permit testing and evaluation of fragrance profiles in vivo reducing reliance on expert panels during product development and it could be applied to assessing the retention of fragrance components on skin to ensure integrity of retention in a diverse range of cosmetic products. Moreover, recent evidence has demonstrated the role that deodorant residues may affect the attractiveness of volatile skin emanations to the malaria mosquito _Anopheles coluzzii_[35]. This highlights the need for further investigation into the impact of cosmetics on the human scent profiles towards development of novel vector control tools.  
**Supplementary Materials:** The following are available online at [[http://www.mdpic.com/2079-9284/5/4/62/s1](http://www.mdpic.com/2079-9284/5/4/62/s1)]([http://www.mdpic.com/2079-9284/5/4/62/s1](http://www.mdpic.com/2079-9284/5/4/62/s1)). Figure S1: Distribution of compound classes in human skin volatile samples. Figure S2: Box plot comparing intra- and inter-participant variance for hexanal; Figure S3: Box plot comparing intra- and inter-participant variance for nonanal; Figure S4: Box plot comparing intra- and inter-participant variance for nonanal; Figure S5: Boxplot comparing intra- and inter-participant variance for \(n\)-decanoic acid; Figure S6: Box plot comparing intra- and inter-participant variance for tetradecanoic acid; Figure S7: Box plot comparing intra- and inter-participant variance for \(n\)-hexadecanoic acid; Figure S8: Box plot comparing intra- and inter-participant variance for isopropyl palmitate; Figure S9: Box plot comparing intra- and inter-participant variance for squalane; Figure S10: Box plot comparing intra- and inter-participant variance for 6-methyl-5-hepten-2-one; Figure S11: Box plot comparing intra- and inter-participant variance for geranyl acetone; Table S1: Measured tissue dielectric constants for participants' skin; Figure S12: Participant scent profiles after addition of fragrance to skin.  
**Author Contributions:** [PERSON] and [PERSON] conceived and designed the experiments. [PERSON] and [PERSON] performed the experiments and data analysis. [PERSON] wrote the paper. All authors approved the final manuscript.  
**Funding:** This research was funded by Science Foundation Ireland, grant number 13/CDA/2155.  
**Conflicts of Interest:** The authors declare no conflict of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript; or in the decision to publish the results.