How does the hair shaft capture drug use?

Drugs which are ingested circulate in a person’s bloodstream and nourish the developing hair follicle.

Trace amounts of the drugs become entrapped in the core of the hair shaft in amounts proportional to the rate of ingestion.

These trace amounts of drugs remain in the cortex of the hair strand as it grows out from the head at a rate of approximately 1-1.3cm per month.

Unlike urine, where drug residues can simply be flushed out of the system, drugs are stable in hair for longer periods of time, creating a drug history.