Question: What is the scientific basis for using nails (fingernails and/or toe nails) as a testing matrix for detecting drugs?
Answer: The cited article notes, “Nails are made of keratin. The average growth rate for fingernails is 3 mm per month (range between 1.9 and 4.4 mm/month). Toenails grow 30 – 50% slower than fingernails and are much more susceptible to drug contamination from sweat. As the nail grows, [some] chemicals (illicit sub- stances, drugs, alcohol biomarkers, etc.) incorporate into the keratin fibers where they can stay for extended periods of time (3 – 5 months in fingernails, and 8 – 14 months in toenails). The mechanisms of drug deposition in nails have not been extensively studied.” (Shu I., et al. Detection of drugs in nails: Three year experience. 2015 J Analytical Tox 39:624-628)