# Chemical Characterization of Human Body Odor Headspace Components
## 4 Discussion  
While whole-human body odor analytical perspectives are not novel, this study corroborates previous studies [17; 18] utilizing chamber collection approaches depicting both nonanal and decanal as key odor markers. In addition, [PERSON] and [PERSON] reported seeing an array of ketones, aldehydes, hydrocarbons, and alcohols, which were also seen in the present study [18]. Ketones, such as 6-Methyl-5-hepten-2-one and 6,10-Dimethyl-5,9-undecadien-2-one; hydrocarbons like hexadecane and tetradecane; and other aldehydes like benzaldehyde and heptanal (in addition to nonanal and decanal) were all shared compounds between the present study and that performed by [PERSON] and [PERSON] [18]. In contrast to this reported study, our collection approach did not yield a high abundance of acids. Similar to the present study, [PERSON] et al. also reported a lack of acid detection among their whole-body sampling [17]. This was deemed to be a limitation of their collection substrate (Tenax-TA tubes) as well as the chromatographic columns used for their analysis [17]. Additionally, [PERSON] et al. [17] focused on VOCs strictly emitted from whole-body skin, and, considering that the skin was the most highly exposed via the chamber odor collection in the present study, these results corroborate those seen in the previous literature. These compound classes have been previously reported as originating from metabolism of skin lipids and bacterial degradation [41]. Given that carboxylic acids tend to be heavier than other groups, this could explain their lack of presence in the current study. The sampling technique via the chamber could have potentially created a headspace too large for the acids to reach the SPME fiber, and thus, only compounds with higher volatility were able to reach the SPME fiber. It is important to note that human scent sampling techniques have intrinsic limitations to the results obtained and, hence, make the reproducibility across studies challenging for result merging. In this particular study, the DVB/CAR/PDMS SPME fiber was utilized for headspace odor sampling. This fiber was selected by the authors in previous studies as optimal for odor collection. However, the large headspace area surrounding the human subject within the chamber yields to variations in the amounts of compounds absorbed by the SPME sampling devices. Future studies should investigate alternate fiber chemistries within this chamber context as well as evaluate higher fiber numbers during sampling to optimize potential vapor sampling limitations of the SPME technique. When comparing the whole body and individual biospecimens, the surface area and body sampling regions can lead to varying VOCs, as different locations have different microbial populations, and thus, different biotransformation processes that result in the release of VOCs [42]. The chamber sampling method allowed for the entire human body to be exposed, thus providing a higher surface area of the human body available for VOC collection. With this enhanced \"body exposure availability,\" a wider range of VOCs could potentially be in the available headspace and available for detection. This can lend a hand in explaining why some compounds were detected via chamber sampling versus individual biospecimens. When the sampling location is reduced to a smaller body part, such as the palms of the hands--which consist mainly of eccrine sweat glands [42]--the biotransformation processes may differ and thus lead to a slightly different odor profile. The constituents of an individual that remain constant across time regardless of diet/environmental factors are termed the primary odor, while the secondary odor is composed of those constituents that are a result of the diet/environmental factors. Lastly, constituents that exist due to outside sources, such as lotions, soaps, etc., are described as the tertiary odor [21]. Therefore, the variation in primary compounds observed between individuals and sample types could be a result of any of these aforementioned factors.