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How Legal Decisions are Made Using Hair Tests: The Foundations of Interpretation

Medico Legal

by Lolita Tsanaclis, Cansford Laboratories

Unpicking the world of hair testing for drug and alcohol can be a complex business. While the scientific community views the practice through a purely scientific lens, it’s a subject that’s equally important to others, like family lawyers and social workers, in terms of its application, results, and the interpretation of those results.

Founded in 1995, The Society of Hair Testing (SoHT) was created by a group of toxicologists from various countries to promote scientific cooperation in the field of testing hair samples for drugs, to promote research in a variety of subjects, and to develop international proficiency tests.

The Society also produces guidelines for laboratories involved in the drug testing of hair: guidelines which cover everything from collection and storage to preparation, pre-treatment and analysis. Here, we delve into these guidelines – last updated in mid-2017 – and analyse what they mean for family lawyers, social workers and family law cases.


Hair drug testing has a variety of applications, providing, as it does, a history of an individual’s exposure to drugs, whether through regular use or as a one-off. These guidelines ensure hair testing continues to be acceptable as a form of evidence in court.

What is the scope of the guidelines?

The guidelines are designed for those already using hair testing and those considering it for the future. For the former, it provides best practice guidelines that are accepted across the globe – for the latter, it outlines the requirements for such testing.

What are the applications of hair testing?

While blood and urine testing can provide evidence of drugs taken recently enough to still be in the user’s system, the makeup of hair tissue means that, depending on its length, it can be used to test for drug presence over a period that spans weeks and months. For this reason, hair testing is a practice used increasingly in family law cases, particularly in care proceedings where there are questions over parental drug abuse. In all cases, hair test results should not be used in isolation and all relevant factors in a case need to be taken into account before any action is taken. The SoHT guidelines set out four cases in which testing tends to be used, namely:

1. Drug-related deaths

Hair testing can provide evidence of chronic drug use prior to death, and also establish whether the cause of death can be attributed to drug usage. Establishing abstinence in the months before death can help to judge tolerance levels to a drug that may be the cause of death, and hair testing can also be used in poisoning cases.

2. Drug-facilitated crime

Drug-facilitated crime, where the victim is administered drugs that may cause amnesia or sedation, can be demonstrated proven through hair testing, which can pick up low levels of the drug, even when the crime has been reported weeks or months after the event. It can also be used to detect drugs such as GHB, used in drug-facilitated sexual assault cases. It’s worth noting, hair testing can demonstrate an association of an event with a drug. But it is not able to prove that a substance was used on a particular time or day. So with drug facilitated crime the hair testing evidence is corroborative not proof.

3. Child custody

Infants and children may be exposed to drugs in a number of ways: through drug and alcohol abuse by the mother in pregnancy, exposure via breastfeeding, access to residue on contaminated surfaces, passive smoking from those nearby and even exposure via contact with the sweat of drug users. Testing for a mother’s drug abuse during pregnancy is possible by collecting a sample of hair from the baby (if it has not been cut since birth) and testing: drugs identified in the hair’s distal region can be attributed to drug use during pregnancy, while drugs picked up elsewhere in the hair suggest exposure post-birth.

4. Chronic excessive alcohol consumption

Two different markers in hair can be used to identify chronic excessive alcohol consumption. Ethyl Glucuronide (EtG) and fatty acid Ethyl esters (FAEEs). Most laboratories are now able to detect levels of these substances that imply chronic excessive use of alcohol over three months or more. A few laboratories can test a lower level that suggests abstinence or at least a very low level of drinking.

However, in their alcohol consensus document the SoHT advise that it is not advisable to use the results of hair testing for alcohol markers in isolation; all relevant factors surrounding a case must be considered when providing expert interpretation and opinion.

However, the levels of these markers can be affected by cosmetic hair treatments (including hairsprays that contain alcohol), so hair tests may form only part of the evidential picture.

Sample collection

Observed sample collection of urine can be embarrassing as very involved procedures are commonly used to ensure the integrity of the sample. On the other hand hair can be collected unobtrusively and can be stored indefinitely. Head hair grows at a rate of 1cm per month, and a pencil thickness of hair is required, at a length that allows accurate testing for the dates in question. Hair can be collected from multiple sites on the head if the subject worries that bald patches will be left, but can also be collected from other areas such as beards, underarms and the pubic area if needed – although characteristics of hair from these areas are different and must be considered in the interpretation of hair test results.

Bleaching, dyeing, and even regular shampooing can affect hair samples. Laboratories must be informed about the condition of each hair sample. Failure can throw results into question.

This section of the guidelines goes on to explain the recommendations for collection processes in a variety of circumstances: a failure to meet these recommendations may mean that the sample is compromised and cannot be used in a family law court case.

Sample preparation

To prepare hair samples for analysis, samples will need to be washed and may also be segmented. Both procedures may affect the accuracy of results.

• Segmentation – By segmenting hair samples, it is possible to understand historical profiles of drug exposure. However, accuracy will depend on the accuracy of sampling and of the lab’s segmentation process.

• Washing – Washing or the decontamination of hair samples allows the laboratory to remove elements such as hair care products, body fluids, sweat, sebum and skin cells that may interfere with analysis, as well as external contamination with drugs. There is currently no standardised washing procedure, but laboratories are expected to use procedures that identify how much surface contamination is removed without removing traces of drugs incorporated into the hair.

Testing procedures

Pre-treatment processes release drugs from within hair. Certain extraction methods can affect specific drug types, so care must be taken here.

Screening is then conducted in one of two ways: either using immunoassays (also used for screening bodily fluids), or chromatographic techniques which screen for a larger number of drugs in a single sample. Tests that are presumed positive are then retested with higher sensitivity levels, as hair drug levels are lower than those found in urine or blood.

Result ‘accuracy’ (in quotations because the word has a variety of meanings) can be damaged each step, and in family law cases, different methods may be used for different case types. There are recommended cutoffs to identify chronic drug use, which vary by drug type. However, in drug-facilitated crime, for example, where it could be that a single claimed occurrence of poisoning is being investigated, lower cut-offs are used to detect a single intake of the drug in question.

Quality assurance and quality control are of vital importance in drug hair testing, with laboratories required to meet specific industry standards as laid out in the Guidelines. It is recommended that laboratories involved in this type of work take part in proficiency testing programmes, which use drugpositive hair samples to compare results given by different laboratories for the same sample.

Hair testing has a wide range of applications in family law; from providing evidence in child abuse cases to establishing whether a mother has taken drugs during pregnancy. The method produces reliable and accurate results, providing that everything from sampling to analysis is carried out in the right way.

The Society of Hair Testing Guidelines ensure hair testing results can be used as legal evidence – but, as with any test type, mistakes are possible along the way. The more family lawyers understand about hair testing and its details, the better.

Dr. Lolita Tsanaclis has been working in the field of hair testing since 1993 and is a leading authority in the field. She is the Scientific Director of Cansford Labs, Cardiff and a member of the Society of Hair Testing (SOHT); the London Toxicology Group (LTG); and of The International Association of Forensic Toxicologists (TIAFT). She can be contacted at This email address is being protected from spambots. You need JavaScript enabled to view it.

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