A century of hair clippings show lead exposure rates have plummeted

A century of haircuts shows lead exposure rates have fallen

By Meghan Bartels edited by Claire Cameron

Your hair can tell scientists a lot more than whether you’re having a good or bad hair day.

Hair “is really a storehouse of information,” says Ken Smith, a demographer at the University of Utah. He should know: He’s part of a team of scientists who analyzed chemicals found in hair samples collected over more than a century in a study published Feb. 2 in Proceedings of the National Academy of Sciences USA. Surprisingly, Smith and his colleagues found that exposure to lead, a dangerous heavy metal, had fallen more than 100-fold since the 1960s.

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The study is small and limited to the greater Salt Lake City, Utah area. But it shows how physical memories such as strands of hair hidden in albums for decades can reveal how our environment has changed over time.

The researchers collected 47 hair samples dated from 1916 to 2024 and enlisted Diego Fernandez, a geochemist at the University of Utah, to analyze the hair’s lead content. The analysis did not distinguish between lead present in the sheath-like cuticle that surrounds a hair and that present in the hair itself. The first would have been captured by contaminated air, and the second would come from the consumption of contaminated food or water.

The trend over time is astonishing. The peak lead levels occurred in samples from the 1960s, when lead was enriched about 120 times compared to samples from 2020 to 2024. But since the 1960s, lead exposure rates have steadily fallen.

This decline occurred alongside the creation of the Environmental Protection Agency in 1970 and the passage of landmark laws, including the Clean Air Act and Clean Water Act, during the same decade, although researchers also note that the greater Salt Lake City area was home to two smelters that closed during this period.

Yet the decline is staggering. “I think it’s kind of a coup to show the power of environmental protection,” Smith says.

Katarzyna Kordas, an environmental epidemiologist at the University at Buffalo who was not involved in the new research, agrees. “We think we need big studies to be able to show trends, and this study indicates that we can still, with a small group of people, see things remarkably clear.”

Kordas notes that much of the best research on lead levels has used blood samples to assess exposure, and that the studies only date from the last decades of the 20th century. By tapping into biological information stored in people’s souvenir hair strands, Smith and his team were able to push back this timeline.

Although the study results suggest the extraordinary success of clean air and water laws, the researchers warn that any gains in lead exposure could be reversed if pollution policies change. Any level of lead exposure is dangerous, with health consequences that include cognitive problems and learning difficulties in children as well as kidney and cardiovascular problems later in life, Kordas says. And even today, some people in the United States remain exposed.

“As a toxin, lead is serious, and we should certainly be concerned about it and work to reduce population exposure,” Kordas says. “I don’t think we can let our guard down and say, ‘This is a solved problem.'”

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