When it comes to drug testing , few methods are as accurate and reliable as the hair follicle drug test . Unlike urine or saliva tests, which have shorter detection windows, a hair drug test can reveal substance use up to 90 days prior. This makes it a popular choice for employers, legal systems, and even rehabilitation programs. If you're facing this kind of test or simply want to understand how it works, this detailed guide will walk you through everything you need to know. 🔍 What Is a Hair Follicle Drug Test? A hair follicle drug test involves analyzing a small sample of hair—typically from the scalp—to detect the presence of drug metabolites , which are byproducts left in the body after a substance is broken down. These metabolites travel through the bloodstream and are deposited into hair follicles, where they remain as the hair grows. Once collected, the hair sample (usually around 1.5 inches in length) is tested in a lab for common controlled substances such as: M...