Why Do Hair Drug Tests Go Back 90 Days?
Hair drug tests are commonly used to detect the presence of drugs in a person's system. One question that often arises is why these tests typically look back 90 days. This guide will answer this question and provide an understanding of the process.
Why 90 Days?
Hair grows at a consistent rate, with the average person's hair growing about 1.25 inches per month. This consistent growth allows for a timeline to be established based on the length of the hair sample. As drugs are absorbed into the bloodstream and eventually into the hair, they can be detected in hair follicles that have grown during the time of use.
Drugs in the Hair
Drugs remain detectable in hair for an extended period because hair is made up of keratin, a protein that is not easily metabolized by the body. This means that once drugs enter the hair follicle, they can stay in the hair for several months, making it possible to detect drug use over a long period of time.
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Testing Accuracy
Testing hair for a period of 90 days is considered a reliable method due to the slow and steady nature of hair growth and the long-lasting presence of drugs within the hair shaft. This duration allows for the detection of most substances, providing a comprehensive view of potential drug use.
why do hair drug tests go back 90 days
Limitations
While a 90-day test is reliable, it does have limitations. For example, it cannot detect recent drug use, as drugs must have had time to enter the hair. Additionally, some individuals may have faster or slower hair growth rates, which can affect the accuracy of the test.
Conclusion
Hair drug tests look back 90 days due to the slow growth rate of hair and the persistence of drugs within the hair shaft. This duration allows for accurate detection of drug use over a significant period, though it is not without limitations.