# Determination and Profiling of Human Skin Odors Using Hair Samples
## 4 Discussion  
By applying the same sampling method and method for VOC extraction and analysis, the present study identified 37 VOCs from three volunteers residing in an urban area (Salvador City) and 42 VOCs from 33 different subjects residing in a rural area 275 km from Salvador, reaching a total of 49 identified compounds. It is important to observe that studies in which the extraction step was performed in a confined space, as in headspace solid-phase microextraction with no external interferences (e.g., surrounding air) resulted in the detection of 20-90 VOCs [8; 9; 24; 25; 26]. Therefore, the resulting 49 identified compounds acquired in the present study are in accordance with this interval. Previous studies have reported high quantitative and qualitative variability of human skin VOCs. Such variability has been associated with a diversity of factors, such as the region of the body that is considered for analysis and the methods applied to investigate the skin odor profile [1], although the sampling method is presumed to be the largest factor. Indeed, different methods and different numbers of subjects have been utilized in several studies, as outlined in this section. As mentioned above, the methods adopted in the present study resulted in a total of 49 detected VOCs, while more than 400 VOCs were already detected and identified as released from human skin odors. However, until now, the highest numbers of VOCs detected were achieved by combining different methods or by including a large number of subjects, as reported by [PERSON], [PERSON], andYost and [PERSON] and colleagues, whose studies resulted in 303 VOCs detected by using glass beads exposed to skin for a few minutes by four different volunteers and 373 VOCs detected by exposing PDMS-coated stir bars to the sweaty armpit surfaces of 197 volunteers [13; 14]. Glass beads were also applied by [PERSON] and colleagues by rubbing these beads against the feet of 48 volunteers, which resulted in the identification of 15 VOCs [5]. The methods applied by [PERSON], [PERSON], [PERSON] and by [PERSON] and colleagues required approximately 10-15 min of rubbing glass beads to collect the skin VOCs [5; 13], which can be unpleasant for the volunteers and demand a long time for sampling. The 373 VOCs reported by [PERSON] and colleagues, however, were obtained by collecting samples five times from each of the 197 volunteers that participated in this study, which also required a great deal of time and effort by the researchers [14]. Another study that may be relevant to be mentioned here was produced by [PERSON] and colleagues, who investigated the human skin VOCs obtained by four different methods, from a total of 26 subjects: (1) Solvent extraction from blades used for scraping heels; (2) SPME fiber exposure upon feet enclosed inside plastic bags; (3) contact SPME, by directly placing the fiber upon the skin of the feet; (4) and using a dynamic headspace that functioned by enclosing the feet in a system that allowed for VOC adsorption by a polymer, such as a purge and trap system [9]. In this investigation, atotal of 44 VOCs were detected, most of which were detected by all four methods. In another study, aPDMS membrane was directly applied to the back, forearm, anthigh of one unique individual and 99 VOCs were identified, 27 of which were detected in all three body areas [23]. All the methods mentioned here showed efficiency in collecting VOCs related to human skin odors. However, as observed in other studies that used, for example, sweat, gauze, cotton, or t-shirts exposed for periods of time (minutes, hours, and eleven several days) to collect VOCs, all of these approaches have many inconveniences.