The persistence of moisturisers on skin

Abstract

Forensic trace evidence in sexual assault casework can be used to corroborate or refute statements from the accused, the complainant, or witnesses. Currently, there are established standard operating procedures for forensic analysis of lubricant trace evidence, but there are no such procedures optimised for investigation of moisturiser trace evidence. There have been sexual assault cases facilitated with a moisturiser bought to the attention of The Institute of Environmental Science and Research New Zealand. The first aim of this research was to create standard protocol for analysing trace moisturiser evidence in case of future cases. The moisturiser trace evidence protocol created used Gas Chromatography - Mass Spectrometry analysis to quantify the amount of common moisturiser ingredients on human skin. Once a protocol was established, a participant centred study was performed to determine the persistence of moisturisers on human skin - for how long after application can moisturisers be detected when using this protocol. Two moisturisers were used in the study; a glycerol-based moisturiser; Aveeno Active Naturals® Daily Moisturising Lotion, and a petrolatum-based moisturiser; Dermatological E45 moisturising lotion. Sampling was performed on the forearms of participants. Modelling from the participant study calculated that the Aveeno moisturiser will persist on average for 19.75 hours ± 1 hour, and the E45 moisturiser will persist on average for 13.5 hours ± 45 minutes. These persistence time frames rival the persistence found in condom lubricant studies, and indicate that moisturiser trace evidence is worth pursuing further to be applied to casework. However, the persistences calculated from the modelling were longer than those seen practically, which were up to 15 hours for the Aveeno and 10 hours for the E45. In addition, the effect of some activities on moisturiser persistence on the forearm were assessed. Exercising or washing will reduce the persistence of moisturisers, while having the forearm covered with fabric (sleeves or sheets) will increase the persistence of moisturisers. The value of the change in persistence was dependent on the moisturiser ingredient. Overall, moisturiser evidence has great potential as trace evidence in sexual assault cases, and should be researched further.