A hair test looks for drug metabolites deposited in the hair shaft as it grows, which gives it a detection window measured in months rather than days. That is the entire reason employers buy it, and it is also the reason it is controversial and why federally regulated testing does not use it. This page covers what it detects, what it misses, and where it is and is not appropriate.
The detection window, and what it really means
A standard hair specimen is taken close to the scalp and the length analysed is usually about one and a half inches, which corresponds to roughly ninety days of growth. That is a much longer look-back than urine, which detects most substances for a few days. But the window has a blind spot at both ends: hair takes several days to grow out of the scalp, so very recent use may not appear at all, and the test tells you about a period rather than about impairment on any particular day. An employer looking for current impairment is using the wrong instrument.
What it is good and bad at
Hair testing is difficult to defeat by short-term abstinence or by the dilution tactics that affect urine, and it gives a picture of a pattern rather than a moment. Against that, it does not reach very recent use, alcohol is not detected in the same way, and there is longstanding scientific debate about whether external contamination and hair colour or texture can affect results, which is one reason it has been the subject of employment litigation. A positive hair result is normally confirmed by mass spectrometry, and a responsible programme offers a urine test alongside rather than treating hair as the sole evidence.
Why federally regulated testing does not use it
Testing conducted under Department of Transportation authority follows 49 CFR Part 40, which specifies urine, and oral fluid where authorised. Hair is not an authorised specimen for DOT testing, so a hair result cannot satisfy a regulated testing requirement however thorough it is. Employers with both regulated and unregulated populations sometimes run hair testing for the unregulated group and the federally specified procedure for the regulated one, which is lawful but means two programmes and two sets of records.
What it costs
Hair testing is consistently more expensive than a urine panel, because the analysis is more involved. Like every panel test it is bought from a collection and laboratory network rather than from the background screening providers whose prices this site records, so it is quoted separately and per test. Ask whether the quoted figure includes the collection, the confirmatory analysis and the Medical Review Officer review, because those three are itemised differently by different vendors and a headline figure that excludes two of them is not a price.
Questions people ask about hair follicle test
How far back does a hair follicle test detect drug use?
About ninety days, based on the roughly one and a half inches of growth analysed. It does not reliably detect use in the last few days, because hair takes time to grow out of the scalp.
Can a hair test be used for DOT testing?
No. Regulated testing under 49 CFR Part 40 specifies urine, and oral fluid where authorised. Hair is not an authorised specimen for it.
Is a hair test more accurate than urine?
It is harder to defeat and covers a longer period, but it answers a different question. It shows a pattern over months rather than recent use or impairment, and it has been challenged over external contamination and hair type.
How much does a hair follicle drug test cost?
More than a urine panel, and it is quoted per test by the collection and laboratory network rather than by a background screening provider. Ask whether collection, confirmation and Medical Review Officer review are included.