Hair Strand and Nail Testing in Care Proceedings: Where are we, two years on from Re: D?

This article is written by Max Melsa as part of the August 2026 edition of the Family Law Dekagram (newsletter).

I had the privilege of being involved in Re D (Children: Interim Care Order: Hair Strand Testing) [2024] EWCA Civ 498 in which the Court of Appeal further clarified the correct approach to hair strand testing in care proceedings. Two years on, I am still finding that test results are being queried and scrutinised in many different ways, and with varying success. What has also become a theme, at least in cases I have been involved in, is the increased use of nail testing as opposed to hair testing – particularly given how intrusive the provision of hair samples can be.

What Is Hair Strand Testing?

I am not a scientist in any shape or form; however, practitioners do need to have at least some knowledge of how these tests work so that they can interpret them at Court.

In simple terms, Hair Strand Testing works by analysing chemicals called metabolites that become trapped in hair as it grows. These metabolites can reveal whether someone has used drugs or consumed excessive alcohol over a period of three to supposedly twelve months (although I have only ever seen results for up to about six months), depending on how long their hair is.

Nail testing works in a similar way and can provide evidence of substance or chronic excessive alcohol use.

What are the difficulties?

As the Court of Appeal said in Re D “The science of hair-strand and nail testing for prescribed and non-prescribed drugs and alcohol has contributed to family court decision-making for many years.”

However, neither test is perfect. Test reports usually include the raw scientific data, supported by a written opinion by the expert explaining what the data means. Courts have become increasingly concerned about gaps between what the raw data actually shows and the expert’s written opinion.

The complexity of the pages and pages that come with the test results themselves, as well as the lengthy opinions of the experts, who use what can be quite confusing language at times, means that for practitioners with limited time to read them at urgent hearings, instructed at the last minute, they can be an absolute nightmare to interpret.

What Have the Courts Said?

Re D exemplified how Courts can put too much weight upon the results of Hair Strand Testing. The Court of Appeal looked closely at three test reports and found problems with how the expert’s written opinions matched up with the underlying scientific data.

Peter Jackson LJ also referred to two earlier High Court cases—Islington v M and Re H—which highlighted “recognised and inherent occasional anomalies in hair strand testing science.” The Court found that hair strand testing sometimes produces unexpected or unreliable results, and that judges need to keep this in mind, especially when making decisions about removing children from their parents’ care at the interim stage.

The key message from Re: D is not that hair strand testing should be banned or ignored; but they should be carefully examined to ensure that the expert’s opinion truly matches the raw data. The results should also not be relied upon too heavily without any other evidence – especially when deciding whether to remove children from their families. It is just one piece of evidence that needs to be considered alongside everything else.

Why Aren’t Tests Always Reliable?

1. Environmental contamination: A person might test positive not because they used drugs, but because they were around drugs. For example, being in a room where cannabis was smoked, or spending prolonged time on a balcony next to a neighbour smoking cannabis; even the regular handling of items such as banknotes contaminated with drugs like cocaine; could produce a positive result.
2. Hair treatments: Bleaching, dyeing, or chemical treatments can break down the substances in hair that the test looks for. This could lead to a false negative (the test says no drugs were used when they actually were) or inaccurate readings. Parties are now warned through various wording (depending on what Court the proceedings are in) not to dye their hair from the date of the direction until the date of the sample being given. Inevitably, this is regularly not followed. Adverse inferences are becoming much more regular in these cases.
3. Differences between people: Hair grows at different rates in different ethnic backgrounds, and factors like hair thickness and hair colour can affect how well substances are absorbed and retained. This means two people who used the same amount of a substance might get different test results.
4. Interpretation: It is not always possible to tell from the data alone whether someone has used a substance once or many times. The courts have been particularly concerned about the difference between what the raw numbers show and what the expert writes in their opinion.

What About Nail Testing?

Again, I am no scientist. However, nail testing works by analysing fingernail or toenail clippings. Nails are made of a hard protein called keratin which absorbs substances from the bloodstream as it grows. The test can detect drugs and alcohol markers (such as a substance called ethyl glucuronide, EtG, which indicates alcohol consumption).

Nail testing has also been used in the family courts for many years. It is usually used when hair is not available – for example, if a parent shaves their head – or when hair is too short to test. It can also be used to back up or challenge hair strand test results, or as an alternative when hair treatments make hair samples unreliable. I have had experience of Rastafarian parents not agreeing to cut their hair on religious grounds.

How Does Nail Testing Compare with Hair Testing?

The detection window is similar for both methods: hair can be up to twelve months; typically, fingernails can provide between three to six months; toenails can be up to twelve months.

A key advantage of hair testing is that hair can be cut into sections to show a rough month-by-month timeline of substance use (since hair grows at about 1cm per month). Nail testing cannot easily do this (indeed, I have never seen it). Fingernails grow at about 3-4mm per month and toenails at about 1-2mm per month, and so there is a wider range for discrepancies.

In regards to potential contamination, substances enter the nail through several different routes, making it hard to pinpoint exactly when someone used a substance. An advantage of nails is that they are not affected by hair dye or bleach; but nails may be more likely to pick up contamination from direct contact with substances – for example, through the handling of drugs.

Are Nail Tests Reliable?

The courts apply the same rules to nail testing as to hair strand testing, which means that the court must look at how the sample was collected; whether there could have been contamination; and whether the expert’s conclusions are supported by the data.

There are some specific concerns with nail testing, as alluded to above. Substances can enter nails through the blood, sweat, and from the outside environment, which makes it harder to prove that a positive result means someone actually consumed a substance.

What Is Being Done About These Concerns?

The Family Justice Council – an advisory body that helps improve how family courts work – has set up a dedicated Hair Strand Testing Working Group. The Working Group is developing best practice guidance for courts; reviewing research, looking at report templates from different testing providers, and gathering information from local authorities about their policies on hair strand testing.

What Does This Mean in Practice?

For lawyers representing parents: Re D gives strong support for challenging hair strand test evidence, especially at the interim stage. Lawyers should question whether the expert’s conclusions match the raw data, and can raise the problems mentioned above, as well as argue that children should not be removed based on test results alone.

For local authorities: The message is one of caution. Hair strand test evidence is still valid and useful, but applications to remove children that rely mainly on test results are at risk of being overturned on appeal. Local authorities should make sure they have a broader range of evidence and deal honestly with any inconsistencies in the test data.

For children’s guardians: There is a need to carefully examine all the evidence. Guardians should consider whether the test evidence has been properly questioned and whether further expert input is needed before making a recommendation.

Conclusion

To answer the question posed as the title of this article – where are we now? The answer: pretty much where we were back in May 2024. This article was not written simply to waste your time, however (honest); hair strand testing and nail testing remain important tools in care proceedings. But be warned – the law around how they should be used is likely to change once the Family Justice Council report on it. In the meantime, Re D remains the first port of call – the courts must look at both hair and nail test results carefully and critically, not treat them as automatic proof.