A common limitation to most forensic trace evidence analysis is the ability to determine the time at which the evidence was deposited at the crime scene. This issue of timing is vitally important as it may not only reveal when the crime occurred, but could exclude potential suspects from the investigation. Using a reverse transcription quantitative polymerase chain reaction (RT-qPCR) assay, the authors monitored the relative expression ratio (RER) of two different RNA species (18S and -actin) in hair samples that were aged naturally over a period of 3 months. No gender or age-of-donor biases were observed, and results were linear up to 60 days. After 60 days, the results were more variable and gave unreliable estimates of time since deposition. Overall, the results presented in this paper suggest that the age of hair samples containing follicular tags can be approximated using a second-order polynomial, although with limitations: Age = 3.31RER2 - 2.85RER - 0.54 (R2 = 0.98). (Published Abstract)