Hair testing for drugs and alcohol. It’s fast, accurate and can detect substance use dating back months.
But what about baldness?
Often, potential users dismiss hair testing on the grounds that their donor has no head hair. Many turn to nail testing as an alternative – a testing method which is still being evaluated scientifically*.
Nail testing can certainly be effective in assessing drug and alcohol over weeks or months, but you may not need it. Even bald donors can be hair tested, using hair from their body.
In 2017, our sister laboratory, Chromatox, supported the Brazillian Government to hair-test 57,000 professional drivers in the country. 60.4% of these tests were conducted using body hair.
The fact is, body hair is as accurate a marker of drug and alcohol use as head hair. There are differences between the two types, however, which users commissioning tests should be aware of. Here’s what you need to know.
How body hair tests work
Tests on body hair work in the same way as those taken from the head.
First, collection. A GP or trained collector cuts a hair sample from the individual, from anywhere on the body and as close to the root as possible. An independent witness must be present to ensure collection is done properly and samples have not been swapped or tampered with. This sample – of around 4mm thickness – is wrapped in aluminium foil and sent, sealed, to the test laboratory in a specialised envelope.
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Laboratory scientists then use chemicals to break down the sample. The resulting solution is then tested to determine if a named substance is present in the sample. Test methods differ between laboratories. For more on the best-in-class LC/MS-MS technique used at Cansford Labs, click here.
The scientist performing the test then uses the test result to make their judgement of if and when the donor used or was in the presence of the named substance.
Why body hair testing is different
Head hair grows from the scalp at a rate of around 10mm each month. As such, a 10mm section of hair can be analysed to prove whether the donor used or was exposed to a substance within the month the section comes from.
On average, hair from different parts of the body also grows around 10mm a month, within a wider level of variation. However, more body hair exists in the ‘resting’ biological phase than in head hair (between 40% and 60% of body hair, as opposed to 10% - 15% of head hair). In this ‘resting’ – or ’telogen’ – phase, hair is present above the skin but it is not growing.
This means that the estimation of time period covered by the body hair is more approximate than head hair. As such, body hair samples are typically not cut into 10mm sections to indicate substance use or exposure within a specified timeframe. Body hair samples can only indicate whether the donor used, or was exposed to, a substance during the life of the hair – that is, since the donor shaved the area the hair was taken from.
Body hair can show evidence of substance use over a much longer period than head hair. This does not mean body hair tests should be used to achieve longer ‘testing windows’, however. A laboratory cannot determine if, when or whether a body hair is, or was, in its ‘growing’ or ‘resting’ phase. This being true, the fact that body hair covers a longer period than the theoretical value determined by the hair length is a good indication that the user does not use drugs when the test is negative.
To baldly go
Both head and body hair tests are equally accurate. Tests on head hair have the added advantage of indicating approximately when substance use or exposure occurred, which is why laboratories recommend testing head hair where possible.
It’s important to note, however, that body hair tests are useful and scientifically reliable – and preferable to not testing, or to using a less established method like nail testing. Unlike hair testing, which is conducted according to global guidelines set by the Society of Hair Testing, nail testing has no such international standard and therefore offers less robust evidence for use in courtrooms.
Users commissioning tests must understand the different interpretations possible with body hair tests, compared to head hair tests – and they must inform their laboratory about the context for the sample to achieve a fair and accurate result.
Baldness is no excuse to miss a hair test. Find out about the other ways donors try to avoid being tested – and why they won’t work – here.
*The exact incorporation mechanism for drug incorporation into hair and nails is not sufficiently understood as incorporation takes place via nail matrix and nail bed (two layers the nail lays upon).
Studies indicate that nail scrapings are less suitable than nail clippings. The window of detection in nail clipping, therefore, depends on nail length, to suitably be used for retrospective monitoring of drug history alternatively to hair, especially in cases where hair is not long enough or cosmetically treated.