Latent fingermark aging: Chemical degradation over time

This chapter presents an overview of the current knowledge regarding the chemical composition of fingermarks and its modification as a function of time, focusing primarily on the compounds targeted in fingermark detection and/or age estimation purposes. As numerous studies have been published regarding these constituents in various contexts, this discussion will pertain mainly to fingermarks and human skin secretions, with some in vitro experiments where relevant additional information is provided. Thus, chemical degradation of the main eccrine (e.g., water, amino acids, proteins, lactic acid) and sebaceous (e.g., fatty acids, triglycerides, wax esters) components will be detailed, including illustrations of molecular structures, degradation mechanisms, and products. Four main factors affecting the chemical degradation of fingermark components will also be described, namely, the initial chemical composition (i.e., variations due to interactions between fingermark components, donors' characteristics, and transfer conditions), the nature of the substrate, the environment (i.e., variations due to light, air flow, water and ambient humidity, temperature, and microbial activity), and time. Finally, key elements to be considered when conducting fingermark aging studies will be discussed.