Hair tests detect substances in a person’s system over an extended period. This article explains how these tests work and whether secondhand smoke exposure can be detected through hair analysis.
How Hair Tests Detect Chemical Exposure
Chemicals circulating in the bloodstream become incorporated into hair as it grows, as hair follicles absorb substances from the blood supply and deposit them into the hair shaft. Hair analysis typically examines the section of hair closest to the scalp, providing information about substance exposure over a specific timeframe, commonly up to 90 days for a standard 1.5-inch sample. Laboratories analyze both the parent chemical and its metabolites, compounds produced when the body breaks down a substance. Metabolites are often more stable and remain detectable longer than the original substance. For example, nicotine, a component of tobacco smoke, is metabolized into cotinine, a more reliable and persistent marker for tobacco exposure.
Detecting Secondhand Smoke Components in Hair
Hair tests detect components of tobacco smoke, including nicotine and its metabolite, cotinine. Cotinine is the primary marker because it remains in the body longer than nicotine. The presence of cotinine in hair indicates exposure to tobacco smoke, whether from active smoking or from secondhand smoke. Distinguishing between low-level secondhand exposure and active smoking can be complex. However, quantitative analysis, which measures compound concentration, provides valuable insight. Active smokers typically exhibit significantly higher levels of cotinine in their hair compared to individuals with only passive exposure. For instance, one study found median hair nicotine concentrations for active smokers around 16.2 ng/mg, while passive smokers had median levels of about 0.36 ng/mg. Nevertheless, substantial and prolonged secondhand smoke exposure could lead to detectable levels, potentially exceeding certain thresholds.
Interpreting Hair Test Results for Smoke Exposure
When interpreting hair test results for smoke components, cotinine concentration levels are important. While cotinine is detectable from secondhand exposure, the amount found helps differentiate between active smoking and environmental exposure. For example, cotinine levels above a certain threshold, such as 0.8 ng/mg, have indicated active smoking in some studies, though specific cut-off values vary between laboratories. A positive test for cotinine indicates nicotine exposure, but it does not definitively confirm active smoking, especially at lower concentrations. Levels of cotinine in hair for non-smokers with passive exposure can vary, with some studies detecting nicotine at concentrations around 1.38 ng/mg and cotinine at 12.8 pg/mg in the hair of non-smokers. Context is crucial for accurate interpretation, particularly in employment screenings or legal cases. The duration and intensity of secondhand smoke exposure directly influence detectable cotinine levels in hair.