Hair "Records" Where You've Been, Study Finds

Joab Jackson
for National Geographic News
February 26, 2008

The chemical makeup of your hair can reveal where in the world you've been, researchers have found.

Water molecules found in human hair closely resemble those in the tap water people drink, according to a new study by University of Utah researcher Thure E. Cerling and his colleagues.

Such a link could provide evidence of where a person has spent the last few months, thanks to water's tendency to differ slightly in its chemical makeup from one latitude to the next.

Researchers have long known that water contains different ratios of chemical signatures, called isotopes, in different regions of the world.

Since water is a principal ingredient in hair, the researchers hypothesized that the hair itself should reflect a person's geographic location.

"For years, hair records diet information with carbon and nitrogen isotopes," Cerling said. "This research shows that geography is recorded as well."

To test their idea, the researchers collected hair samples from barbershops in 65 cities in the continental United States. They also took samples of the tap water in these locations.

They found an 85 percent correlation between the isotope ratios in the hair and those in the tap water.

The researchers report their results in this week's issue of the Proceedings of the National Academy of Sciences.

Barbershop Clues

An isotope is a chemical compound with a different number of neutrons than the normal form of that compound. A "light" water isotope has fewer neutrons than what researchers call a heavy isotope.

The varying distribution of isotopes in water is so predictable that scientists have drawn up maps showing ratios of various isotopes around the world.

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