# Chemical Characterization of Human Body Odor Headspace Components
## 1 Introduction  
Canines are a vital biological detector tool for various law enforcement agencies, with different detection applications including explosives, narcotics, human remains, and human scent [1]. Human scent itself can be described as a mixture of numerous volatile organic compounds (VOCs) released from the skin, breath, and bodily fluids, resulting in a highly varied human biochemistry that can be analyzed via noninvasive approaches with appropriate headspace instrumental techniques [2, 3, 4]. As a form of trace evidence, human scent can aid in criminal investigations by determining the travel direction of a suspect, identifying the suspect through a scent line-up procedure, or aiding in victim search and recovery efforts [3]. This type of evidence is commonly paired with human scent detection canines, because these biological detectors are specifically trained to identify and locate the scent of live humans [5]. Although a plethora of research within human scent detection disciplines already exists, there is a current gap in understanding the odor picture of the constituents of the human body that are of importance for canine response and perception. Therefore, it is important to understand the volatile odor chemical characterization of a whole human and how it may differ from the chemical odor profile of individual biospecimens (hand, axillary, breath), to understand and better inform sensor development and canine human scent detection. In 2014, a study reported a total of1846 compounds across different biospecicns from healthy individuals to include a range of chemical classes, such as aldehydes, short- and long-chain hydrocarbons, carboxylic acids, alcohols, esters, ketones, and amines [6]. Further work in the human volatilome continued with over 900 new compounds being reported in an updated compendium in 2021 [7]. While the study of human scent has increased over the years, it is important to understand the complexity of this type of analysis. Many variables come into play, including instrumental headspace analysis techniques, methods and body area of collection, subject characteristics (gender, lifestyle, medical history), and environment. Hence, human scent odor signatures are complex and dynamic, posing a challenge for chemical and biological detection. Chemical odor characterization in support of canine detection has been performed on a wide variety of target odors, with human scent being one of the main sources of study. Human scent is a widely utilized canine detection discipline within law enforcement and search and rescue operations [8]. Human scent detection canines can be used to establish an association between human scent traces left at a given location or in pre-scenting scenarios in which the canine is given a scented article to follow an associated scent trail to a specific person or location. Within search and rescue applications, a more generalized definition of human scent is the target for detection, as the canine's goal is to locate live human victims in disaster events for victim recovery efforts. [PERSON] et. al., for example, took the approach of general body odor sampling through sensor arrays to better understand the \"entrapped\" human odor signature for natural disaster situations [9]. Human scent detection can be broadly categorized into (1) generalization of a live human scent odor signature and (2) individualization of a specific subject in a discrimination scenario. Regardless of the application, a central gap in knowledge with respect to human scent detection is the identification of the human volatile markers perceived by dogs to make the identification or, even yet, the most productive compounds for sensor development in cases of technology advancements aiming to help first responders locate victims in disaster environments [9]. Volatolomics is a current area of much research in many different applications to understand the composition, origin, and detection of volatile biomarkers from the human body.