The simple answer is hair drug testing can go back as far as the hair shaft is long. So, if a 3cm section of hair provides an approximate 3-month overview, a 12 cm section of hair can offer an approximate 12-month profile.
The Timeline of Hair Follicle Testing
While a urine test typically has a detection time frame of 2-5 days, a hair follicle test can detect drug use as far back as 90 days. For this reason, it is considered a more reliable indicator of drug use than urine testing.
Bleaching, dyeing, perming, and straightening can all impact a hair drug test result. This is because the chemicals used in these types of treatments can damage the hair shaft and alter the concentration of the drug.
The use of a drug on one occasion only would not be expected to give rise to positive results as insufficient drug would be expected to accumulate in the hair to be detected above the cut off level. This is because almost all of the hair analysed would cover a time when drug use had not occurred.
Specificity of hair testing at standard laboratory cut-offs exceeded 90% for all drugs, but sensitivity of hair testing relative to self-report was low, identifying only 52.3% (127/243) of self-disclosed marijuana users, 65.2% (30/46) of cocaine users, 24.2% (8/33) of amphetamine users, and 2.9% (2/68) of opioid users.
Up to 90 days can fail a hair follicle test.
While abstaining from drug use is the only surefire way to pass a hair drug test, awareness of the test's capabilities and limitations is essential for informed decision-making.
Some methods of attempting to cheat a hair drug test include shaving all body hair, using a detox shampoo, or bleaching or dyeing the hair. However, these methods are not effective and result in detection of the tampering efforts (which can have negative repercussions, especially in legal cases).
Some of the methods include shaving all of the hair off, detox shampoos, and home remedies including substances like tar shampoo, laundry detergent, detox salts, and vinegar. Some people even dye their hair after using these remedies to help mask the changes made to their hair.
Bleaching hair peroxide decreases the detectability of cocaine in user hair. Melanin–cocaine bonds are broken and cocaine is degraded into reaction products. Unbound cocaine and reaction products are washed out removing evidence of cocaine use.
Given adequate hair length, hair testing can detect exposure to psychoactive substances within wide time-frames – much wider than with urine, blood, and saliva. However, hair testing cannot detect very recent exposure, and infrequent cannabis use in particular can be difficult to detect.
Hair drug testing on dyed or bleached hair may still be worthwhile. Any chemical treatment such as hair dye, bleach, chemical straightening and permanent waves can damage the hair. This damage may lead to some of the drugs that may be present, being leached out from the hair.
This is because it takes about 5-10 days for drug-containing hair to grow above the scalp. Will one night of drinking show up in a hair follicle test? No, a single night of drinking will not show up in a hair follicle test. However, regular and heavy alcohol consumption can be detected in hair samples.
How far back can a hair drug test detect drug use? Hair drug tests have the longest detection period, and can typically detect drug use for up to 90 days. Depending on the drugs used, a hair sample can sometimes help determine when drug use occurred and whether it's been discontinued.
Hair testing can only detect drugs that have been consumed; it cannot detect drugs that have been injected or breathed. This is a crucial point to keep in mind.
According to the results of the study, hair follicle drug testing correctly identified: 52.3 percent of people who reported recent cannabis use. 65.2 percent of people who reported recent cocaine use. 24.2 percent of people who reported recent amphetamine use.
Hair drug test collection
If the donor does not have head hair or if their hair is less than a ½ inch long, a specimen can be taken from other locations on the body. In order of preference, our collectors will cut the chest, underarm, leg, or facial hair to obtain a sample.
An evidentiary false positive that is the result of exogenous exposure to drug(s) in the environment. The drug positive result is not due to the ingestion or use of drug by any route of administration. Drug(s) in sweat or sebum from a source other than the user contacting hair to cause a drug positive result.
For a person smoking marijuana for the first time, tests may identify it for around three days. For a person who smokes marijuana 3-4 times per week, the detection window is 5-7 days. For a person who smokes marijuana daily, tests may detect it for 30 days or longer.
2 In general, the detection time is longest in hair, followed by urine and oral fluid. 2 Drugs in hair may be detectable for approximately 90 days, whereas drugs in urine are generally detectable for one to seven days or longer in chronic users and in oral fluid from five to 48 hours.
Hair drug testing and bleached hair
Bleaching the hair can remove between 40-80% of metabolites found in the hair strand. If multiple bleaching attempts are made a participant can remove all drugs from their hair. A worrying situation and one of the reasons why so many “blonds” arrive at sample collections.