Hair Analysis Reveals a Century of Lead Exposure and the Impact of Regulation

For millennia, humans have utilized the heavy metal lead, but its widespread toxic effects were not well understood until the last century. A new study of preserved human hair samples now provides clear physical evidence of the severity of past public exposure to lead. The research also demonstrates the remarkable effectiveness of government regulations, enacted once the dangers were recognized, in significantly reducing that exposure.

Published in the journal PNAS, the study analyzed hair from 47 individuals who lived in the Greater Salt Lake City area of Utah. Participants provided locks of their baby hair, saved in family albums, as well as current samples from their adult years. By examining these samples, scientists constructed a record of lead exposure spanning approximately a century. "We have hair samples spanning about 100 years," said study co-author Ken Smith, a demographer at the University of Utah.

The research team employed a technique called mass spectrometry to measure lead levels in the hair. This method can identify and measure specific chemical compounds within a sample with a high degree of accuracy.

Lead exposure is harmful to human health in multiple ways. It damages the nervous system, which can lead to developmental delays, learning difficulties, and seizures. It also elevates the risk of high blood pressure and fertility problems. Crucially, scientists state there is no known safe level of exposure to lead.

During the first half of the 20th century, a primary source of this toxic exposure was leaded gasoline. In the 1920s, a compound called tetraethyl lead was added to fuel to prevent engine "knocking," a pinging sound caused by premature fuel ignition. Although U.S. health officials recognized problems with leaded fuel as early as 1925, it was not completely banned in the United States until 1996.

The new study found that key environmental regulations established before the 1990s had an immediate and powerful impact. The most significant change coincided with the creation of the U.S. Environmental Protection Agency (EPA) in 1970.

Lead concentrations in the hair samples from the Salt Lake City region were exceptionally high from 1916 to 1969. This was due partly to the absence of EPA regulations and partly to the operation of two active lead smelting plants in the area. However, from the 1970s to the 1990s—after the EPA was formed and the smelters closed—average lead levels in hair dropped dramatically.

"Current concentrations of lead in hair from this population average almost 100 times lower than before the establishment of the Environmental Protection Agency," the researchers reported. This decline represents a reduction by two orders of magnitude, a massive decrease.

The study offers strong evidence that environmental policies grounded in science can successfully control dangerous pollutants.

One important distinction in the research is that the amount of lead detected in hair does not correspond precisely to the level in a person's blood. Blood lead level is the standard metric doctors use to determine if someone requires treatment for lead poisoning.

However, hair provides a unique long-term record of environmental exposure. A hair sample "doesn't really record that internal blood concentration that your brain is seeing, but it tells you about that overall environmental exposure," explained study co-author Thure Cerling, a geologist at the University of Utah.

The data unequivocally show that people were absorbing far greater quantities of lead from their environment prior to 1970. "It's just coming out of the tailpipe, goes up in the air and then it comes down," Cerling said. Lead particles can linger in the atmosphere for days. "It absorbs into your hair, you breathe it, and it goes into your lungs."

The researchers concluded their study with a warning. They noted that while their work demonstrates the success of past regulations, such rules are now at risk of being weakened or eliminated.

They specifically referenced a 2025 announcement by the EPA and then-President Donald Trump. That announcement aimed to deregulate numerous EPA provisions designed to ensure clean air, land, and water. While it did not specifically mention lead, experts suggested it represented a "roadmap" for rolling back rules on air pollution from factories and wastewater from coal plants. At least one federal lawsuit was filed to challenge parts of this plan.

"We should not forget the lessons of history," Cerling cautioned. "Those regulations have been very important." He observed that the EPA had "really, really positive effects" very quickly after its creation.

The study of historic hair reveals that the relaxed environmental standards of past decades resulted in unhealthy lead exposure. Yet, it also proves these hazardous levels can be controlled through what the researchers term "science-based regulations."

In the contemporary United States, the threat of lead exposure has shifted but not disappeared. It now poses the greatest risk in low-income communities and in older cities in the Northeast and Midwest. Housing constructed before 1978—the year lead-based paint was banned—is a primary concern. Other common sources include soil contaminated by historical mining or industrial activity, old pipes and plumbing, and even some imported toys, jewelry, or candies. Young children under the age of 6 are especially vulnerable to lead poisoning because their developing bodies absorb the metal more readily.

Cerling, T.E., Fernandez, D.P., & Smith, K.R. (2026). Lead in archived hair documents a decline in lead exposure to humans since the establishment of the US Environmental Protection Agency. PNAS, 123, e2525498123.