A century of hair clippings shows lead exposure rates have declined
There’s no safe level of lead exposure—but a small, strange study shows we’ve made incredible progress in recent decades.
Francis McLaughlin-Gill/Condé Nast via Getty Images
Your hair scientists can tell you a lot more than just whether your hair is having a good or bad day.
Ken Smith, a demographer at the University of Utah, says hair is “really a storehouse of information.” He should know—he’s among a team of scientists who analyzed chemicals found in hair samples collected over more than a century in research published Feb. 2. Proceedings of the National Academy of Sciences, USA. Incredibly, Smith and his colleagues found that Exposure to lead – a dangerous heavy metal – has declined more than 100-fold since the 1960s.
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The study is small and limited to the greater Salt Lake City area of ​​Utah. But it shows that physical mementos like a lock of hair hidden in a scrapbook for decades can reveal how our environment has changed over time.
Researchers collected 47 hair samples from 1916 to 2024 and called in Diego Fernandez, a geochemist at the University of Utah, to analyze the amount of lead in the hair. The analysis found no difference between the lead present in the cuticle like sheath that surrounds the hair and the lead found in the hair. The first may have originated from contaminated air, and the second may have originated from consumption of contaminated food or water.
The trend over time is surprising. The highest rates of lead were seen in samples from the 1960s, when lead was enriched approximately 120 times compared to 2020-2024 samples. But since the 1960s, lead exposure rates have declined steadily.
This decline coincided with the formation of the Environmental Protection Agency in 1970 and the passage of landmark legislation in the same decade, including the Clean Air Act and the Clean Water Act, although researchers also note that the Greater Salt Lake City area was home to two smelting facilities that closed during that period.
Still, the decline is astonishing. “I think it’s kind of a showstopper to show the power of environmental protection,” says Smith.
Katarzyna Kordas, an environmental epidemiologist at the University at Buffalo who was not involved in the new research, agrees. “Our belief is that we need larger studies to be able to show trends, and this study is indicating that we may still be seeing things that are remarkably pronounced in a small group of people.”
Cordas says most of the best research done on lead levels has used blood samples to measure exposure, and the studies date only to the latter decades of the 20th century. By tapping into the biological information stored in people’s memorable hair, Smith and his team were able to push back that timeline.
Although the study results indicate extraordinary success of the Clean Air and Clean Water Act, researchers warn that all the benefits of lead exposure could be reversed if pollution policies are changed. Cordas says lead exposure at any level is unsafe, with health consequences that include cognitive problems and learning difficulties in children and kidney and heart problems later in life. And even today some people in America remain naked.
“As a poison goes, lead is serious, and we should certainly be concerned and try to reduce population exposure,” says Cordes. “I don’t think we can let our guards down and say, ‘This is a settled issue.'”
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