Hair Analysis [en Español]
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Hair analysis can be used to check if people are blood relatives. Forensic hair analysis can be done to help identify a criminal by evaluating hair structure and DNA from cells attached to the root of the hair. Hair samples are tested with specific chemicals and looked at under a microscope. Hair analysis can also be used to check for poisoning caused by metals such as lead or mercury. But hair analysis alone usually is not used for this type of testing.
Hair is a protein that grows out of hair follicles in the skin. Normally, a hair grows in the hair follicle for many months, stops growing, and falls out. A new hair then grows in the follicle. It takes weeks for a hair sample to show changes in the body, because hair grows slowly. Hair samples do not show recent changes in the body, such as drug use within the past few days. But a hair analysis may show drug use or exposure to chemicals that occurred over the last few months.
Why It Is Done
Hair analysis is used to provide DNA evidence for criminal and paternity cases. For DNA testing, the root of one hair is needed to analyze DNA and to establish a person's genetic makeup.
Hair analysis is less commonly used to test for heavy metals in the body, such as lead, mercury, and arsenic.
How To Prepare
If you have a hair analysis done, the laboratory will give you specific instructions on how to prepare your hair. Hair preparation and the part of your body from which the hair is taken varies. In general, your hair should be washed and free of any hair care products.
You may be asked to sign a consent form that says you understand the risks of the test and agree to have it done.
Talk to your doctor about any concerns you have regarding the need for the test, its risks, how it will be done, or what the results may mean. To help you understand the importance of this test, fill out the medical test information form (What is a PDF document?) .
How It Is Done
Hair analysis is done by collecting a hair sample and sending it to a laboratory. If a DNA test is done on the hair, then the hair collected needs to have the root attached.
Hair samples are taken from a specific part of the body, such as from the back of the scalp by the neck or from the pubic area. Hair samples are generally collected from the section of the hair closest to the skin. Hair close to the skin or scalp includes the most recent growth, which provides the most accurate information about what has occurred recently in the body.
Hair samples are washed in special chemicals before testing.
Hair samples for DNA analysis will be gathered by laboratory personnel or law enforcement officials or a forensic examiner . For DNA testing, the hair must include the root. This requires that the hair be plucked, not cut.
Heavy metal analysis
If you are collecting your own hair sample, follow the instructions given to you by the laboratory. In general, you will be asked to:
- Clip a small sample of your hair (usually about a spoonful) from the nape of your neck. The sample should be 1 in. (2.5 cm) to 1.5 in. (4 cm) long and should include the new growth closest to the scalp.
- Put the clippings in a plastic bag and seal it.
- Send the samples to the laboratory along with information about the type of hair treatments you have used, including shampoos, conditioners, colorings, bleaches, and permanents. Information about your age, height, weight, sex, and whether you smoke may also be requested by the laboratory.
How It Feels
There is generally no pain or discomfort associated with this test. But if you have to pluck a hair for a DNA test, this may cause some minor discomfort.
Hair analysis itself has no risks or complications.
Hair analysis uses samples of hair for DNA analysis or to look for heavy metals, such as lead or arsenic.
Heavy metal analysis
The results of hair analysis are usually complete within 3 weeks. You or your doctor will receive a report listing the levels of minerals and heavy metals in your hair. Several things need to be considered before testing for heavy metal exposure.
There is no standard procedure for cutting, washing, and analyzing hair. Different labs may report different results from the same hair sample. In fact, the same lab may report different results for separate hairs from a common sample. Standards for testing do not exist. Any hair analysis to detect the presence or absence of minerals, nutrients, or toxic metals in the body should be confirmed by testing blood and urine samples.
What the hair sample contains is determined not only by nutrition and internal metabolism but also by external substances. Air pollution, mineral content of the water supply, exposure to industrial waste, shampoos, hair dyes, hair sprays, permanents, and bleaches may raise or lower the levels of certain minerals in the hair. Also, the use of medicines such as birth control pills can change the mineral concentration of hair.
What Affects the Test
Things that can interfere with your test and the accuracy of the results include:
- The area of the body from which the hair sample was taken.
- Your age.
- Your hair color.
- Your race.
- The rate of your hair growth.
- Your use of hair products, such as hair colors and sprays.
- External environmental factors, such as where you live and work.
What To Think About
- Hair analysis has become more reliable and acceptable over the past 20 years. But there are still issues that raise legal and ethical questions about its use, including possible false positives and different results for people with different hair colors or ethnic backgrounds.
- Some natural health and homeopathic companies offer hair analysis by mail order. But hair analysis is not a accurate way of determining your need for vitamins, minerals, or other nutrients.
- The importance of most of the findings from hair analysis is unclear. It is hard to interpret a hair analysis for the presence of heavy metals without other testing. For most trace minerals, what really means normal or significant deviations from normal is not known.
- Although hair analysis is being done more frequently to test for illegal drug use (such as the use of cocaine or marijuana), it is not widely available. Drug screening is more commonly done on blood or urine samples. To learn more, see the topic Toxicology Tests .
Other Works Consulted
- Curtis J, Greenberg M (2008). Screening for drugs of abuse: Hair as an alternative matrix: A review of the medical toxicologist. Clinical Toxicology. 46: 22–34.
- Fischbach FT, Dunning MB III, eds. (2009). Manual of Laboratory and Diagnostic Tests, 8th ed. Philadelphia: Lippincott Williams and Wilkins.
- Vassiliki BA, et al. (2006). Hair as a biological indicator of drug use, drug abuse or chronic exposure to environmental toxicants. International Journal of Toxicology. 25: 43–163.
Primary Medical Reviewer E. Gregory Thompson, MD - Internal Medicine
Specialist Medical Reviewer R. Steven Tharratt, MD, MPVM, FACP, FCCP - Pulmonology, Critical Care Medicine, Medical Toxicology
Current as ofAugust 21, 2015
Current as of: August 21, 2015
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