Your hair can tell scientists a whole lot more than whether you’re having a great hair day or a terrible one.
Hair “is really a vault of information,” says Ken Smith, a demographer at the University of Utah. He should know—he’s among a team of scientists that analyzed chemicals found in hair samples collected over the course of more than a century in research published on February 2 in Proceedings of the National Academy of Sciences USA. Incredibly, Smith and his colleagues found that exposure to lead—a dangerous heavy metal—has fallen by a factor of more than 100 since the 1960s.
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The study is small and limited to the greater Salt Lake City region of Utah. But it shows how physical mementos such as locks of hair stashed in scrapbooks for decades can reveal how our environment has changed over time.
Researchers gathered 47 hair samples dated from 1916 to 2024 and called in Diego Fernandez, a geochemist at the University of Utah, to analyze the lead content in the hair. The analysis didn’t distinguish between lead in the sheathlike cuticle that surrounds a hair and that found in the hair itself. The former would have been picked up from contaminated air, and the latter would have stemmed from the consumption of contaminated food or water.
The trend over time is stunning. Peak lead rates occurred in samples from the 1960s, when lead was enriched by some 120 times compared with 2020–2024 samples. But since the 1960s, lead exposure rates steadily plummeted.
The decline occurred alongside the formation of the Environmental Protection Agency in 1970 and the passage of landmark legislation, including the Clean Air Act and the Clean Water Act, in the same decade, although the researchers also note that the greater Salt Lake City region had been home to two smelting facilities that closed during that period.
Still, the decline is stunning. “I think it’s kind of a showstopper for showing the power of environmental protections,” Smith says.
Katarzyna Kordas, an environmental epidemiologist at the University at Buffalo, who was not involved in the new research, agrees. “We have this notion that we need large studies to be able to show trends, and this study is indicating that we can still in a small group of people see things that are remarkably clear.”
Kordas notes that much of the best research on lead levels has used blood samples to gauge exposure, and the studies date only to the later decades of the 20th century. By tapping biological information stored in people’s keepsake locks of hair, Smith and his team were able to push that time line back.
Although the study’s results hint at the extraordinary success of the Clean Air and Clean Water Acts, the researchers warn that all the gains in lead exposure could be reversed if pollution policies change. Any level of lead exposure is unsafe, with health consequences that include cognitive issues and learning difficulties in children and kidney and cardiovascular problems later in life, Kordas says. And even today some people in the U.S. remain exposed.
“As a toxin goes, lead is serious, and we should certainly be concerned and striving to lower population exposure,” Kordas says. “I don’t think that we can let our guards down and say, ‘This is a solved issue.’”