Can External Cocaine Rubbed Into Hair Survive Shampooing Yet Fail a Wash-Criterion Test?

What did the researchers actually test?

This original study examined how externally deposited cocaine behaves when hair is physically rubbed with drug powder, wetted with a synthetic perspiration solution, washed repeatedly with consumer shampoo, and then subjected to the laboratory’s own extraction and interpretive procedures. A parallel in-house experiment used two initially negative brown hair lots. A government-sponsored cooperative project supplied five additional prepared hair samples; the authors analyzed those received in their laboratory and compared the patterns.

Neither experiment assigned cocaine to a living volunteer. The applied powder, bath and shampoo schedule were laboratory manipulations of collected hair. There was no controlled oral, smoked, intravenous, intranasal or dermal human dose. A recorded cocaine mass on a hair strand cannot be recast as a known person’s exposure, ingestion, drug effect or bodily concentration merely because the specimen originally came from a human donor.

How many independent humans were involved?

The operative experimental units were two in-house hair lots and five separately treated cooperative-study hair lots. The source does not establish seven independently enrolled cocaine-exposed people. Cutting each lot into many analytical aliquots, collecting weekly subsamples, or repeating injections creates correlated technical measurements of material from a given lot, not new independent participants. Similarly, the three laboratories in the cooperative work are analytical settings, not additional human subjects.

This matters whenever a graph contains dozens of dots or the Table 1 protocol lists three replicates per time point. The replicate values describe within-material heterogeneity and analytical behavior. They cannot support a prevalence statement about users or a population confidence interval for whether external exposure will be misclassified. The study’s experimental strength is process interrogation, not a large independent biological sample.

Was the drug administered or merely applied to the hair?

The researchers applied powdered cocaine hydrochloride by controlled rubbing. The cooperative project specified 15 mg per 12 g hair, and the in-house experiment used 5 mg per 4 g hair: both are a nominal 1.25 mg cocaine hydrochloride per gram of hair before later losses. The nominal preparation ratio must not be mistaken for a measured retained dose, a user’s inhaled or ingested amount, or a plasma concentration.

Applying powder involves uneven contact, mechanical damage to cuticle structures, and losses during later handling. A chemical present on or inside a hair shaft after rubbing is still externally introduced in this experiment. Even penetration into porous material does not create evidence of systemic absorption by a person. The source tested an experimental origin that was already known to be external; it did not need to infer that origin from real case histories.

Why did the protocol include synthetic sweat?

After rubbing, the hair was sprayed on both sides with a laboratory synthetic-sweat mixture and dried for several hours. Its reported recipe contained sodium chloride at 65 mM, potassium chloride at 5 mM, sodium lactate at 9 mM and urea at 22 mM. That formulation helped mimic a moist environment in which deposited drug might migrate, but it did not collect or measure living human perspiration or actual sweat-gland excretion.

Moisture can alter distribution across a strand. In the larger cooperative series, several hair lots appeared to have more measurable cocaine at the post-sweat sample than immediately after rubbing. The authors discussed uneven rubbing, handling losses, sample porosity and storage conditions as possible contributors. These changes are not evidence that external cocaine was biologically generated by hair. They show why a single pre- versus post-treatment number may not have an intuitively monotonic direction.

How often was shampoo used?

Investigators lathered the hair with a commercial shampoo for several minutes, rinsed it with warm water and dried it. They repeated shampoo treatment on weekdays, taking aliquots after approximately each five treatments, through about four weeks in the in-house experiment. Shampooing is distinct from the much longer laboratory decontamination and extraction procedure used at each analytical time point.

The cumulative schedule models repeated washing under selected laboratory conditions, not ordinary personal hygiene histories. The study did not randomize hair donors by real-world product, measure each donor’s natural hair growth, or evaluate cosmetic chemical processing prospectively in a cohort. Differences observed between its two in-house lots and five cooperative lots therefore should not be generalized into a fixed number of showers after which cocaine will disappear from every type of hair.

What did LC–MS/MS physically measure?

The laboratory used liquid chromatography coupled with tandem mass spectrometry (LC–MS/MS), including an API 2000 triple-quadrupole mass spectrometer operated with multiple-reaction monitoring. The target compounds included parent cocaine, benzoylecgonine, cocaethylene and norcocaine. Under the published assay, the reported limit of detection and limit of quantification were both 0.2 ng per 10 mg of hair for those targets, with a calibration interval reported as 0.2–200 ng per 10 mg.

All reported cocaine amounts are tied to the mass of extracted hair. A figure such as 7.2 ng/10 mg cannot be converted into 7.2 ng/mL of venous whole blood, serum, saliva or natural sweat. The two different quantities represent different specimens and physical denominators. No paired legally collected human venous whole-blood cocaine concentrations were assayed, and the original study provides no conversion coefficient or impairment threshold.

What is the six-stage laboratory wash?

At each collection point the authors weighed roughly 11–13 mg aliquots and washed them before digesting and analyzing the residual hair. The initial step used 2 mL dry isopropanol at 37°C for 15 minutes. The subsequent five phosphate-buffer/BSA washes used 2 mL per cycle at approximately pH 6: three 30-minute cycles, then two 60-minute cycles, for 3.5 hours of aqueous washing. The final aqueous rinse was retained for quantitative analysis.

This procedure is not equivalent to rubbing the hair once with an alcohol swab or washing it in a sink. It uses successive solvents and timed mechanical mixing, followed by digestion and instrumental measurement. The last wash is especially important because its analyte amount enters a separate interpretive calculation. A confirmed parent-cocaine peak remaining after these six steps is an analytical observation, not automatically a conclusion that cocaine came from someone’s blood.

How was the additional wash criterion calculated?

The authors did not rely on the concentration remaining in digested hair alone. Their wash criterion compared the hair cocaine measured after the six washes with a multiple of cocaine appearing in the last phosphate-buffer rinse. The stated subtraction was: post-wash hair cocaine − (5 × cocaine in the last aqueous wash), all expressed consistently as ng/10 mg hair. The fivefold term modeled an additional washing challenge; it was not a human half-life calculation.

For example, in one externally treated aliquot, 7.2 ng/10 mg cocaine remained in hair after laboratory washing while the last rinse contained 11.7 ng/10 mg on the source’s normalization. The calculated residual was 7.2 − 5(11.7) = −51.3 ng/10 mg using the displayed rounded figures (the original table prints approximately −51.1). The negative arithmetic value does not mean the hair contained physically negative cocaine. It means the rule failed decisively: the measured last-wash burden exceeded the amount remaining when extrapolated as that method requires.

What thresholds were required for a use-positive interpretation?

In addition to its last-wash subtraction rule, the published laboratory classification used a hair cocaine cutoff of 5 ng/10 mg, benzoylecgonine of at least 0.5 ng/10 mg, and a benzoylecgonine-to-cocaine ratio of at least 5%. The cocaine wash-adjusted result also had to reach the method’s 5-ng/10-mg interpretation boundary. Multiple conditions had to be considered together; a parent-cocaine result by itself was not the complete decision rule.

These values characterize the authors’ historical laboratory protocol and study. They are not universal statutory thresholds, and benzoylecgonine formed under environmental or storage conditions cannot be treated as an error-free test of voluntary ingestion. The contamination experiment tests whether this specified combination classified these particular artificially exposed materials correctly. It does not validate perfect performance for every hair type, laboratory, cosmetic process, or case allegation.

Evidence table 1: what changed with sweat and four weeks of shampoo?

The following rows reorganize one representative measured aliquot per time point from each of the two in-house hair lots in the source’s original Table 1. They are not averages, new participant counts, biological drug elimination rates, or independent samples. The separate columns compare total material before the long laboratory wash with remaining cocaine after that wash.

The authors judged all treated samples in this comparison negative for an ingestion-associated classification under the combined laboratory criteria. Lot 1’s post-wash parent cocaine exceeded 5 ng/10 mg at certain earlier steps, but its metabolite and wash-criterion results did not support classifying it as drug use. Lot 2 was below the post-wash cocaine cutoff at some time points from the beginning, underscoring material variability.

Why does a value above the parent-cocaine cutoff not settle the interpretation?

A frequently misleading shortcut is to see 7.9 ng/10 mg cocaine after decontamination, compare it with a 5-ng/10-mg cutoff, and declare that a drug user was identified. For these prepared specimens, the analyst already knew the source: cocaine had been applied externally. The complete rule also considered measured benzoylecgonine, its proportion relative to cocaine, and the drug recovered in the late aqueous wash. None of the artificially contaminated aliquots fulfilled the full positive-for-use interpretation.

That outcome is a method-specific finding, not a demonstration that cocaine cannot enter hair from external exposure or that every contamination can be recognized. Conversely, the observation that an externally rubbed specimen can retain more than a parent-cocaine cutoff after cleaning shows why chemical detection and causal origin are logically distinct. A forensic opinion needs evidence connecting a specified molecule in a specified specimen to the claimed route of entry.

Did one hair lot retain cocaine longer than the other?

Yes, despite the same nominal applied powder-to-hair ratio, the lots differed. In the original in-house series, one lot had several post-wash aliquots still at or above 5 ng cocaine per 10 mg in early weekly samples and fell below that level by week four. In the second lot, post-wash measurements were already below 5 ng/10 mg after the first week; some were below the parent cutoff even before synthetic-sweat application. The total cocaine measurements also declined at different rates.

The time course reflects laboratory shampoo exposure, rubbing uniformity, starting hair condition and washing behavior. It must not be presented as cocaine clearing from the bloodstream over four weeks or as a person’s verified abstinence history. In actual cases, drug incorporation from systemic ingestion, scalp and sweat deposition, additional contact, cosmetic treatment and hair cycling may interact differently. This experiment deliberately isolated one mode of external application and then observed heterogeneous analytical retention.

What was different in the five cooperative hair lots?

The cooperative samples included five externally treated lots prepared under a common contamination procedure. Their initial total cocaine measurements after rubbing varied far more than the nominal identical applied amount might suggest. The report describes measurements spanning roughly 100–1,800 ng cocaine per 10 mg hair before sweat. After the synthetic-sweat step, the range was approximately 500–2,000 ng/10 mg, with four of five lots showing larger apparent amounts than their earlier reading.

These observations caution against using one lot to predict all hair specimens. The cooperative lots frequently retained more cocaine after weeks of washing than the two locally processed lots. The results also emphasize how a nonuniform external rubbing procedure can affect what an aliquot contains. The paper did not demonstrate which fraction of the differences was caused by cuticle porosity, storage humidity, uneven material selection or analytical dispersion, and the authors expressly discussed several competing influences.

Why was hair porosity examined?

Porosity describes how readily liquid can penetrate and interact with a hair fiber. The authors used methylene-blue staining to make relative permeability visible, including observations of strands with differing staining patterns. They also compared a chemically permed aliquot with an unpermed aliquot from the same original hair source. The difference was intentionally induced by treatment, not a comparison of two randomly sampled clinical populations.

Highly porous hair can take up a large quantity of externally presented cocaine under some conditions, and it may also release the compound more readily when exposed to an appropriate solvent. Porosity is not measured by hair color alone, and staining is not a molecular assay for cocaine. The source does not establish that a given person’s cosmetic history can be reconstructed reliably from a single stain, nor that one measured porosity number universally predicts external contamination in litigation specimens.

Evidence table 2: how much did chemical perming change cocaine uptake?

The investigators reported an especially instructive paired experimental contrast: aliquots from the same hair sample were either left untreated or chemically permed, then immersed for one hour in a laboratory cocaine solution. These are hair-treatment conditions, not drug-dosing groups or human exposure outcomes.

The measured contrast was approximately 75-fold (2,126 divided by 28.3). It shows that cosmetic chemical treatment can radically change external laboratory uptake in a selected paired hair source. Both prepared aliquots were nevertheless interpreted as contaminated rather than evidence of ingestion under the original wash criterion. The experiment does not provide a population effect estimate or a probability that a particular tested person’s hair was externally contaminated.

Do the results prove the wash criterion is infallible?

No. In these known externally contaminated materials, the combined cutoff, metabolite and wash-criterion approach avoided the authors’ ingestion-associated positive classification. That is useful evidence of a successful challenge under the specified conditions. But successful identification in two in-house lots and five cooperative-study lots cannot establish the absence of false positives in every future case, nor does it automatically validate equivalent performance at different laboratories.

For broader performance claims, one would want preselected independent hair sources representing different porosity and cosmetic histories, controlled positive biological incorporation and controlled external challenges, appropriate blinded comparisons, reproducibility, defined decision thresholds and quantitative uncertainty. The published work included neither a large prospectively characterized sample of genuine cocaine users nor an independent gold-standard basis for calculating universal sensitivity and specificity. Its scope should remain aligned with its design.

Did this paper test statistical significance or nonsignificance?

The displayed rubbing, washing and porosity findings are presented as experimental concentration trajectories and descriptive method comparisons. The paper does not report formal inferential p-values for the difference between the two hair lots, for the paired 28.3-versus-2,126 result, or for performance of the wash classification across a representative population. It would be inaccurate to call those contrasts “statistically significant” or “nonsignificant” without a defined original hypothesis test.

A numeric decrease, an algorithm returning a negative decision, or a measurement below a cutoff is not a nonsignificant hypothesis test. Likewise, an analytical value of zero in a table should not be treated as proof of chemical nonexistence at every detection limit. The defensible result here is descriptive: the tested known-external specimens did not satisfy this laboratory’s complete ingestion-positive criteria, and different hair materials behaved differently.

Could benzoylecgonine establish cocaine ingestion by itself?

Benzoylecgonine is a cocaine-related metabolite and an important analytical target, but the study’s classification combined its measured concentration and ratio with cocaine and residual-wash information. The authors also discuss environmental and experimental factors that can influence cocaine and metabolite patterns. The presence, absence or small amount of a metabolite should therefore be considered with assay specificity, storage history, wash validation, specimen preparation and the complete case record.

This experiment did not demonstrate that every sample containing a metabolite necessarily came from systemic cocaine use, or that every internally exposed person must satisfy all historical thresholds. Those would require different validation experiments with clearly characterized biological administration and comparator materials. A targeted chemical finding should not be turned into an unqualified accusation of use when its provenance and collection conditions remain contested.

What does this mean for prosecution, employment and disciplinary testing?

A practical forensic review should first distinguish three questions: which chemicals were confirmed, in what amounts and units; what controlled external-contamination and decontamination studies support the laboratory’s method; and what case-specific evidence supports a conclusion about internal administration. Chain-of-custody, hair collection site, segment length, cosmetic treatment, environmental handling, product contact, method validation, final rinse measurements, calibration and ion identification can each matter. No single reported hair number supplies all those details.

In adversarial proceedings, the strongest scientifically supported observation is neither “hair cocaine always proves use” nor “a positive is always contamination.” The original experiment instead demonstrates why laboratory decisions are conditional on a defined analytical method and why residual external cocaine may remain measurable. Attribution of a sample to actual ingestion must be demonstrated using evidence suitable for that source question, not inferred from instrument precision alone.

Can any hair result here establish blood cocaine or acute impairment?

No human subject received a controlled cocaine dose, and the article contains no matched quantitative legal venous whole-blood cocaine measurement, no serial blood kinetics, no separate plasma or serum cocaine profile and no contemporaneous verified driving or psychomotor performance test. The nominal 1.25 mg/g applied to hair, the 10 mg/mL immersion solution and the hair measurements in ng/10 mg are three physically distinct quantities. None is interchangeable with the others as a legal blood concentration.

The experiment also supplies no validated personal clock for cocaine use, evidence of a person’s subjective awareness, a witness-truthfulness assessment, a causation model for a collision, or a determination of whether a person was impaired at a particular time. An expert can describe the source’s analytical contamination challenge and methodological caveats without extending it into these unmeasured biological and legal conclusions.

How should a reviewer treat apparently contradictory wash readings?

Some source tabulated wash-criterion computations become negative after subtracting five times the final rinse measurement. Those signed values are outputs of a decision formula, not chemically measured negative quantities. Furthermore, values recalculated from rounded displayed inputs can differ slightly from the printed formula result. The scientifically proper distinction is between instrument-measured hair content, last-wash content and a calculated interpretation variable.

The cooperative study also reported paradoxical increases in apparent total measured cocaine after artificial sweat exposure in several hair lots. The authors did not prove that cocaine was created during drying. Variable rubbing, swelling, hair condition, handling losses, storage and aliquot selection all create plausible alternatives. Reporting the anomalies as anomalies is more defensible than quietly forcing every time course into a smooth elimination curve.

Seven frequently asked scientific questions

Can cocaine remain detectable after repeated shampooing without proving ingestion?

Yes. In the controlled external-rubbing experiment, several aliquots retained instrument-measurable cocaine even after shampoo and extended laboratory washing. The full metabolite and final-rinse interpretation rule nevertheless classified the known externally contaminated specimens as not positive for ingestion. That outcome is specific to these materials and the chosen method.

Were two or seven people actually dosed with cocaine?

No. Two in-house hair lots and five cooperative-study lots were chemically treated after collection. The source does not establish seven independently drug-dosed humans. Repeated cuts, replicate chemical injections and time points measure related laboratory material rather than additional exposed people.

Does a concentration of 7.2 ng per 10 mg hair equal a blood result?

No. The hair quantity is mass of cocaine relative to weighed hair. No matched venous whole-blood cocaine concentration, plasma concentration, time after ingestion or validated matrix-conversion model was measured. Hair values cannot be used as a legal blood concentration.

What if the wash-criterion calculation produces a negative number?

A negative result from hair cocaine minus five times the last-rinse cocaine is a calculated indicator that the prescribed rule does not pass. It does not mean the specimen physically contains negative mass or that the instrument reported a negative concentration.

Does benzoylecgonine alone distinguish all environmental contamination from use?

No. In the reported method benzoylecgonine was only one part of a combined concentration, ratio and wash-based interpretation. Source provenance, contamination chemistry, laboratory validation and case-specific records remain essential; the experiment did not establish universally perfect discrimination.

Were the 75-fold porosity result and week-by-week declines statistically significant?

The original study reported descriptive measurements for these comparisons, not corresponding formal inferential significance tests. There is no support for inventing p-values, declaring a statistically significant population effect or labeling missing tests nonsignificant.

Can this study establish when a driver used cocaine or caused a crash?

No. It applied cocaine hydrochloride externally to collected hair and measured laboratory hair analytes. It included no controlled human administration, legal venous blood testing, individual drug-use time, driving performance, crash investigation or case-causation endpoint.

Original empirical reference and related specimen guidance

Hill V, Cairns T, Schaffer M. Hair analysis for cocaine: Factors in laboratory contamination studies and their relevance to proficiency sample preparation and hair testing practices. Forensic Science International. 2008;176:23–33. Read the original primary DOI and source record. For matrix distinctions, consult the independently published biological-matrices guide; for targeted chemical identification, consult the published confirmatory-testing guide. Both are contextual explanations, not substitute experimental cohorts or missing validation of a personal cocaine-use date.

Bottom line: artificially rubbed cocaine survived shampoo and some rigorous laboratory washing in several hair aliquots, while these known-external samples failed the authors’ combined ingestion-positive decision rule. Hair porosity and handling changed measured retention dramatically. Source-specific method validation is indispensable, and no human blood-drug level, exact ingestion time, individual impairment or incident causation follows from this experiment.