By Anna Sandiford 17/09/2015

Hair analysis is often referred to as hair follicle testing. It is commonly used in Family court matters to assess whether or not parents or caregivers who want access to children are drug-free.

The process involves collection of a sample of hair (usually from the crown of the head but other areas are possible) by a trained hair sample collector and then analysing the hair for the presence of drugs.

Hair analysis is often claimed to be the perfect solution to the question of determining historic drug use or abuse. Segmental analysis is said to determine use over a period of time – on average for adults a centimetre of hair is said to represent a month’s growth so analysing a strand of hair that is 10 centimetres long would reflect the subject’s use of drugs over the ten months or so prior to sampling.

However, in real life nothing is a simple as it is claimed. The incorporation of drugs into the growing hair shaft is dependent on a number of factors including the colour of the hair and the chemical nature of the drug. Further complications are introduced by washing, sweating and the grease in sebum (the oil that is found on hair). Thus washing may remove some of the drug especially from the surface layers of the hair which are opened by moisture. Sweat does the same but it may also contain traces of drugs and thus can add to or remove drugs from the surface layers depending on the relative amounts in the hair and the sweat. Sebum can perform a similar function and thus complicate the distribution of drug along the hair shaft even more.

Chemical treatment such as bleaching or perming may also reduce the drug concentrations in the hair shaft. Environmental contamination such as smoke, dust or vapours containing the drug may further complicate the picture. This is said to be addressed by washing the hair before analysis and then analysing the washings and comparing the results with the segmental analysis to assess the extent of contamination.

Therefore the interpretation of segmental drug analysis in hair should be done with these factors in mind and, despite the court’s preference for results to be black-and-white, we may be working in shades of grey and it may not always be straightforward…

[prepared largely by Dr Alex Allan, Forensic Science Consultant]

Featured photo credit: David Goehring – flickr