Impact of liquid antibacterial soap and hand sanitizer on DNA transfer in forensic investigations: an experimental study

DNA transfer, whether intentional or not, is becoming an important part of forensic evidence gathering and analysis. This study seeks to determine the impact of liquid antibacterial soap and hand sanitizer use on the DNA present in the palms of hands that may potentially reduce direct transfer. Twelve volunteers were enrolled and typed. Afterwards, each palm was swabbed without considering previous activities to collect background DNA profiles. Subsequently, each subject washed his/her hands for 30 s with antibacterial soap first, and after with sanitizing gel and then air-dried them; after drying, each palm was immediately swabbed for DNA typing. The results of this study demonstrated that the possibility of recovering a complete profile from a hand swab is strictly related to previous activity: considering the results of the samples taken before handwashing, there is the possibility of having a median recovery of 80.01%, while it is very low (median recovery was 3.43%) after hand washing with antibacterial soap followed by alcohol-based hand sanitizer. Analyzing the results after handwashing, we were unable to detect any drop-in alleles. Moreover, we determined that in 11/12 samples, less than nine alleles were detected: considering that the kit used for the profiling could analyze 23 short tandem repeats (STRs), it is possible to conclude that we obtained inconclusive profiles. Based on the findings of the present study, it is more difficult to obtain a perpetrator's profile if he/she used liquid antibacterial soap and hand sanitizer immediately before the criminal action.