Hair Analysis for Drugs and Chronic Poisoning

Compounds can reach growing hair through blood-associated incorporation and through sweat, sebum or external material. Their relative contributions differ by analyte and circumstances. The hardened shaft is not a sealed archive that washing or later exposure can never affect.

Physical and chemical properties influence incorporation and retention. Pigmentation can affect some basic drugs, so concentration differences between hair samples do not translate directly into differences in dose. A result should not be used to infer consumption from hair colour alone.

Hair follicles pass through growth and resting phases. Scalp growth near one centimetre per month is a useful average, but individual strands and people vary. A bundle combines hairs with different histories, and the portion below the skin introduces another timing consideration.

Blood, urine, oral fluid, nails and hair can offer different windows. Hair is not the only specimen capable of retrospective information, and body-fluid detection does not end at one fixed number of hours or days for every drug. Select specimens according to the actual question.

Stored or exhumed hair can retain useful evidence, but preservation, contamination and degradation need assessment. A twelve-centimetre sample does not guarantee a complete unchanged twelve-month exposure history. Older distal material has experienced more environmental and cosmetic influences.

Coordinate the required amount, site and segment lengths with the laboratory before collection where possible. Scalp hair from the posterior vertex is generally preferred for timing comparisons because growth varies less there. If another site is used, record it and explain the resulting limitations.

Cut close to the scalp and preserve alignment. Clearly identify the proximal end using a suitable collection system; a particular cotton tie is not the only scientifically acceptable way to retain orientation. A sample with unknown orientation may still be testable, but its temporal interpretation is weakened.

Keep the sample dry and protected from contamination and excessive light under the laboratory's supported storage conditions. Packaging should preserve the strands and identity. Do not present one foil-and-envelope arrangement as a universal legal requirement.

Record colour, available length, collection site, dates and relevant cosmetic or physical treatments. Bleaching, dyeing, straightening and other treatments can alter the target concentration or contamination behaviour. A universal percentage loss cannot be assumed across drugs and treatments.

Body hair can be useful when scalp hair is unavailable or unsuitable, but its growth pattern generally limits segmental timing. Do not assign it a scalp-hair calendar by simple centimetre conversion. Report the different and often less certain interval represented.

Maintain traceable specimen identification and documented transfers. These records support interpretation and review, while the legal consequences of any defect depend on the applicable proceeding and jurisdiction. A documentation gap should be disclosed and assessed for its effect on specimen identity and reliability.

Washing aims to remove interfering surface material and reduce external contamination. The solvent sequence and conditions need laboratory validation; there is no universal three-solvent recipe that removes all contamination while leaving every incorporated analyte unchanged.

Experimental cocaine studies show that contaminant retention depends on exposure conditions and hair properties. Residual material can remain after repeated washing. Conversely, washing can remove some analyte from hair that has experienced systemic exposure, so a wash result has to be interpreted within its validated design.

Wash fractions may help assess contamination, but a falling profile is not proof of ingestion. Interpretive ratios and decision criteria need evidence for the particular analyte and wash procedure. The relevant compounds, their sources and possible degradation need assessment.

Cocaine metabolites can contribute evidence, but some may arise from contamination or conversion. Research comparing consumer hair with occupationally exposed hair supports using a combination of analytes and method-specific criteria rather than one isolated parent concentration.

For cannabis, THC-COOH can strongly support intake within the relevant interpretive framework, but contact and secretions can complicate findings, particularly in children. A compound produced in one person's body can still reach another person's hair through transfer.

The laboratory should explain what its decontamination data and marker findings support. A result can indicate an exposure concern warranting investigation without proving active use, a particular route or an exact administration event.

Segmentation divides an oriented sample into defined lengths. Proximal material generally represents more recent growth than distal material, but calendar boundaries are approximate. Pooling segments can dilute a localised finding and change the period represented by the reported concentration.

Choose extraction conditions for the targets. Pulverisation, cutting, digestion or solvent extraction can affect release and stability. Harsh acid or alkaline conditions can convert labile compounds, potentially altering both recovery and parent–metabolite patterns.

A method tested only with drug added to blank hair may not demonstrate extraction of analyte incorporated during real exposure. Authentic hair controls and appropriate proficiency testing help address the solid, heterogeneous matrix. Calibration and recovery assessment are related but distinct quality tasks.

Chromatography with MS is central to the Society of Hair Testing's confirmation recommendations. The actual identification scheme must suit the acquisition mode, expected concentrations and target. A universal two-transition count or one calibration range cannot be applied to every assay.

Stable-isotope internal standards can help control measurement variability when suitable, but they do not automatically mimic release of drug embedded in authentic hair. Assess selectivity, bias, precision, matrix effects, stability and carryover as part of the complete method.

Report units carefully. One ng/mg equals 1,000 pg/mg. Results in a wash solution volume cannot be directly compared with a hair-mass concentration without the appropriate quantities and calculation. Small unit errors can substantially change a decision.

Separate detection, reliable quantification and a reporting decision. A drug may be measurable below a use-identification cutoff. Conversely, applying a routine-use cutoff to a suspected single exposure can miss relevant evidence. The testing purpose must be stated before interpreting the result.

The SoHT 2021 drug consensus provides target-specific use-assessment criteria and notes a different approach for single or infrequent exposure. Its specified segment-length and metabolite requirements matter. It is not a universal list of clinical impairment concentrations or statutory worldwide thresholds.

Alcohol-marker guidance was revised in 2026. In the specified proximal head-hair context, EtG below 5 pg/mg does not contradict reported abstinence; it does not prove that no alcohol was consumed. EtG at or above 30 pg/mg in a 3–6 cm proximal segment strongly suggests chronic excessive consumption under that consensus.

The 2026 guidance also gives segment-specific ethyl-palmitate criteria as complementary evidence. Different body sites, lengths and storage conditions need care. Do not place one EtG number in a generic drug table and claim it distinguishes every drinking pattern or establishes a diagnosis by itself.

Use the current full consensus for a real decision, including its qualifications. Where a result is close to a decision point, method performance and relevant uncertainty deserve attention. A numerical cutoff does not remove the need for a contextual scientific opinion.

Hair may support selected retrospective elemental investigations, but contamination and interpretation are substantial issues. Water, dust, workplace material or products can contribute external material. A total-element result does not reveal how it reached the hair.

Arsenic interpretation should consider exposure history and suitable blood, urine or environmental measurements where available. A comparison range needs a reliable source with a compatible matrix, analytical method and population. A localised segment peak does not distinguish deliberate poisoning from environmental exposure by itself.

Thallium findings with a compatible clinical course can be important, but alopecia and one hair concentration are not an automatic diagnosis. Blood or urine testing, timing, analytical controls and alternative causes remain relevant.

Metal analysis uses a preparation and detector suited to the measurand. It may require a different specimen aliquot from organic-drug testing. Washing and digestion can affect total-element or species-specific conclusions differently.

A report should distinguish measured concentrations from an inferred exposure pattern. Avoid claiming that nails or hair locate an exposure to a particular week, prove chronic dosing or identify who administered a poison. Those conclusions require evidence beyond the keratin profile.

A useful hair report states the site, segment definition, analytical targets, units, decision framework and limitations. Include relevant collection and cosmetic information and explain the significance of contamination controls. Preserve the underlying analytical records for review.

In a suspected single exposure, timing and sensitivity can be more important than a routine-use cutoff. In repeated-use assessment, multiple segments may add context but cannot reliably quantify each dose. In child-protection work, environmental transfer and the broader safeguarding evidence require particular care.

US, UK and Indian proceedings can apply different legal and professional requirements. Canada, Australia and other jurisdictions also have their own frameworks. A scientific consensus is not a statute, and a laboratory result does not automatically decide employment, custody or criminal responsibility.

Anti-doping, workplace and forensic testing use different rules and specimen frameworks. Confirm that the proposed test is suitable for the actual programme. Hair testing is not an automatically authorised substitute for a blood or urine test, and a finding should be interpreted within its specific purpose.

Related reading: Biological, Non-Biological and Viscera Matrices in Toxicology.

Related reading: Acidic, Neutral and Alkaline Drug Analysis.

Related reading: Toxic Metals and Anions: Arsenic, Lead, Mercury, Thallium and Beyond.