Sunscreens, coconuts and mummified fingers

Sunny, summer days inspire many folks to don swimsuits, blast beach soundtracks, and dive into the hottest seasonal read for a lounge outdoors. Time in the sun helps us make vitamin D3, but overexposure to ultraviolet (UV) light brings sunburns, premature aging and skin cancer. A popular sun safety measure is the use of sunscreens, which often contain titanium dioxide, zinc oxide, oxybenzone or octinoxate. These compounds are found in an array of body care products targeting every area from hair and scalp to the often-forgotten feet. The very prevalence of sunscreens – along with the likelihood they’ll be transferred – renders them potentially important trace evidence that can link persons, objects and places. 

Illuminating such links requires ‘statistically confident methods’ capable of assisting analysts to discern between similar products. Attenuated total reflectance – Fourier transform infrared (ATR–FTIR) spectroscopy, requiring little-to-no sample preparation and being non-destructive in nature, is an increasingly popular technique for a range of forensic applications and often paired with chemometrics. Researchers at Panjab University’s Institute of Forensic Science & Criminology in India have shown the potential of ATR–FTIR spectroscopy paired with principal component analysis to discriminate between sunscreen products. For their pilot study, the researchers analysed over 100 sunscreens directly and developed a model capable of accurately distinguishing all unknown samples. Work evaluating sunscreens transferred onto a limited range of substrates suggests it is also possible to classify sunscreen traces, but a more extensive substrate study is needed.