The persistence of moisturizer products on human skin in relation to sexual assault investigations

Abstract

The use of commercial moisturizers in sexual assault cases has been reported across the globe. Currently, there are limited protocols for the analysis of moisturizers as supporting evidence, and it is unknown if moisturizers persist on skin for forensically-relevant timescales. To better understand the potential for moisturizer evidence to be analyzed as part of a medical examination kit connected to sexual assaults, a participant-based persistence trial was conducted using both glycerol-based and petrolatum-based moisturizer products. Selected target analytes were monitored using GC–MS as tracers of moisturizer persistence: petrolatum, glycerol, cetyl alcohol, isopropyl palmitate, ethylparaben, and methylparaben. The petrolatum-based moisturizer persisted on human skin for 13.5 ± 0.7 h while the glycerol-based moisturizer persisted for 19.8 ± 1 h. Petrolatum had the shortest skin surface lifetime (12 h) while cetyl alcohol had the longest (23.5 h), which may be related to its increased chemical interaction with the skin surface. Exercising and bathing activities correlated with a decrease in moisturizer persistence while skin cover was associated with an increase in moisturizer persistence, meaning the moisturizer lifetimes reported here may underestimate those in covered intimate areas. The observed persistence lifetimes give optimism that moisturizers can be sampled and used as forensic evidence in sexual assault investigations. Through this study, a general sampling and extraction protocol was developed, providing a template that can be used for future work.