how far back can a hair test go
A hair test, also known as a hair follicle test or hair analysis, can detect the presence of substances such as drugs, toxins, or heavy metals in the hair shaft. The length of time that a hair test can detect these substances depends on several factors, including:
- Hair length: The longer the hair, the longer the detection window. Typically, a hair test can detect substances for up to 90 days, but this can be extended to 6-12 months or even longer if the hair is very long.
- Hair growth rate: Hair grows at an average rate of 0.5 inches (1.3 cm) per month. This means that a 1.5-inch (3.8 cm) hair sample can provide a 3-month detection window.
- Substance type: Different substances have different detection windows. For example, marijuana can be detected for up to 90 days, while cocaine can be detected for up to 6 months.
- Test sensitivity: The sensitivity of the test can also impact the detection window. More sensitive tests can detect smaller amounts of a substance, which can extend the detection window.
Here are some general guidelines for the detection windows of common substances in hair tests:
- Marijuana: 30-90 days
- Cocaine: 30-180 days
- Opiates: 30-180 days
- Amphetamines: 30-90 days
- Benzodiazepines: 30-180 days
- Barbiturates: 30-180 days
- Heavy metals: 6-12 months or longer
Keep in mind that these are general estimates, and the actual detection window may vary depending on individual factors, such as hair growth rate, substance use patterns, and test sensitivity.
