Article: When drug metabolites are in the blood, they'll end up in the blood vessels, including those in the head. The traces of the drug then get filtered through the hair, leading to a failed drug test.  Hair drug testing can show the drugs a person may have used over the past several months. It is a more accurate test of long-term drug use than a urine or blood test. A hair drug test involves cutting 50-80 strands of hair from the back of the head, close to the crown. Note that even though the drug test is often referred to as a "hair follicle" test, your skin will not be broken in this test. A minimum length of 1.5 inches of head hair is necessary for the test. If this length of hair is unavailable (such as when the person being tested has a crew cut), body hair such as face, chest, or arm hair can be used. A hair follicle test is a more effective test of long-term or heavy drug use. A single, minor use of a drug is much less likely to lead to a failed hair drug test, though it can happen. If you have only smoked a single joint in the past 3 months, you can be cautiously hopeful that you will pass the drug test. However, if you had a period of time where you smoked a joint every day for a week, you are much more likely to fail the drug test. While a hair drug test is highly effective for past drug use, very recent drug use is harder to detect in this way. It usually takes several days to a week for recent drug use to appear in your hair. For this reason, some employers and agencies will require that you take both a hair test (for long-term drug use) and a urine test (for short-term drug use). One of the more common hair follicle tests is the 5-panel drug test. Like the urine 5-panel test, the hair follicle 5-panel test detects traces of the following drugs:  Marijuana Cocaine Opiates Amphetamines (including ecstasy, meth, and molly) PCP Some employers or legal agencies choose to test for additional drugs outside of the traditional 5-panel test. These drugs include many categories of prescription medication in addition to common street drugs. These drugs include:  Benzodiazepines Methadone Barbiturates Propoxyphene Oxycontin Demerol Tramadol In general, the portion of hair that is tested is the 1.5 inches of head hair closest to the crown of the head. This portion of hair is enough to test your use of drugs in the past 90 days. The only way to be sure to pass a hair test is not to have drugs in your system during this period. Many of the techniques used to fool a urine drug test are not suitable for a hair test. For example, your hair sample is often collected by a lab assistant directly since there are no privacy concerns (as there are for a urine sample). There are no chemical masking agents or dilution methods that can lower toxins in the hair. And a temporary stoppage of drug use is not sufficient to pass most hair drug tests. The very high success rate of the hair drug tests is precisely why many employers and legal agencies use them. It is particularly difficult for people with dark colored hair to fool a hair follicle test. For this reason, there are many claims that hair drug tests are ethnically biased and racist. There are a number of shampoos on the market that claim to help you pass a hair follicle drug test. However, none of these effects have been scientifically proven, and any evidence of their success is anecdotal and possibly suspect.  A potential home remedy that has been rumored to be successful involves rinsing your hair with white vinegar, salicylic acid, and laundry detergent, followed by using a temporary hair dye. This treatment is unproven but is also relatively inexpensive and, as long as you keep these chemicals out of your eyes, has few side effects. Some studies show that cosmetically treated hair is less likely to show traces of cocaine.

What is a summary?
Understand how the hair testing process works. Recognize that hair drug tests are less effective measures of single drug use. Be aware that drugs take 5-7 days to enter your hair. Know the drugs that will be tested for in the 5-panel test. Know other drugs that can be tested for. Stop use of all drugs 90 days before the test. Be aware that hair tests are very difficult to fool. Be cautious about special shampoos and rinses.