Effects of External Contamination and Cosmetic Treatments on Hair Testing Can be Explained…Most of the Time!

Abstract

External contamination of hair with drugs used to be regarded as one of the most questionable points in hair testing, and the risk of false positive as a result of external contamination could see a hair testing result dismissed. Measurements of both hair samples and corresponding wash residue can provide a more reliable indicator of the probability of hair being externally contaminated. The issue of external contamination is manageable in most cases, and it is rare that results cannot discriminate between use and external contamination, but test results will always need to be interpreted in the light of corroborating evidence from “clinical data” or “social context”. We also showed that the results from the analysis of dreadlocked hair samples are useful to provide information on whether the individual has used any substances over an unspecified period. Our data also shows that drug levels are still, in the majority of cases, detected in the hair of regular users even after strong chemical cosmetic hair treatments, although it is always wise to be alert to the possibility of a false negative.