Impact of face-derived DNA on touch DNA deposition on cell phone screens

Advancements in the sensitivity of commercial kits have enabled the genotyping of trace samples, establishing touch DNA as a valuable tool in forensic genetics, especially when fingerprints are absent or lack detail. However, analysis remains challenging due to various factors, including sex, age, surface type, and DNA source. This study investigated whether touching the face before depositing touch DNA on cell phone screens improves the quality and quantity of DNA recovered and assessed the effects of sex, age, and their interaction. Samples from 30 volunteers were collected with and without prior facial contact. DNA was genotyped with the PowerPlex^® ESI17 System. Likelihood ratios were calculated via LRmix Studio. Although the DNA quantity was low, the cell phone screens yielded good-quality profiles. Facial contact significantly increased DNA quantity and allelic match percentages. No significant differences were observed for sex or age, but a statistically significant sex-age interaction was found for allelic match percentages. Males aged 18-29 years exhibited better results than females did in that group for finger-derived DNA; for face-derived DNA, this occurred in those aged 30-49 years. Face-derived DNA provided higher allelic match percentages for both sexes, individuals aged ≥ 50 years, younger females and males aged 30-49 years. Despite the limited sample size, the study illustrates how self-touching behavior can impact forensic DNA recovery. These insights can contribute to a better understanding of touch DNA and highlight the potential for improved identification and misinterpretation depending on the DNA source.