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.
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
You may need 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.
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