A silent danger could be lurking in your home—and toenails are "one of our body’s archives of past exposure," scientists say.
Your toenails already provide a layer of protection on your feet—and new evidence suggests they could also be quietly recording your long-term exposure to a cancer-causing gas in your home. According to November 2025 research published in the Environment International journal, these small clippings may hold valuable clues about cancer risk, especially for people who don’t fit the usual screening guidelines for one particular type.
Lung cancer is often linked to smoking, but another major cause is radon—a radioactive gas that can build up indoors, especially in homes. Radon forms naturally in the ground and can seep through foundations, where people breathe it in over many years. The U.S. Environmental Protection Agency (EPA) reports radon cannot be smelled or seen and that “testing is the only way to know your level of exposure.”
As radon breaks down, it releases radiation that can damage lung cell DNA and raise cancer risk. In fact, long-term radon exposure increases lung cancer risk by about 16% for every 100 units of radon in indoor air, notes the study’s interdisciplinary team of researchers from Canada’s University of Calgary.
The challenge is that many people who develop lung cancer don’t qualify for early screening because they haven’t smoked enough—or at all. According to the American Lung Association (ALA), you might be considered “high risk” for lung cancer if:
- You are between the ages of 50 and 80 years
- You have a 20 pack-year history of smoking (this means 1 pack a day for 20 years, 2 packs a day for 10 years, etc.)
- You are a current smoker, or have quit within the last 15 years
In looking at toenails as a biomarker, the new study marks a novel way to assess this risk. In this study, scientists measured tiny amounts of lead-210, a radioactive byproduct of radon, in toenail clippings from adults. People who had lived for decades in homes with high radon levels had nearly four times more lead-210 in their toenails than those from low-radon homes.
Importantly, higher levels were still found years after people had fixed their homes to reduce radon. Toenails grow slowly, which means they may capture long-term exposure history—not just recent conditions.
“We’ve learned that our toenails hold long-term information about our exposure to radioactive toxicants in our environment such as radon gas. They are one of our body’s archives of past exposure,” said Aaron Goodarzi, PhD, a biochemist and co-author of the study, via news release.
“After you inhale radon, it quite quickly transforms into a specific type of radioactive lead. Your body treats radioactive lead from radon like it does all lead and stores it in slow-shedding tissues such as the skin, hair and nails,” adds Dr. Goodzari, also the Canada Research Chair for Radiation Exposure Disease.
The results were not affected by age, sex, smoking history, or diet, suggesting toenails could become a useful tool for identifying lung cancer risk tied to environmental exposure, rather than relying on age and tobacco use alone. The team is now developing a follow-up study to confirm their preliminary findings.
“If this validation trial works, it could transform the future landscape of cancer prevention,” Dr. Goodarzi says. “The data will form the evidence that could lead to the inclusion of more patients, whose lung cancer is not caused by tobacco smoke, in potentially life-saving early screening and diagnosis.”
While the study suggests a new way to detect lung cancer risk sooner, it also points to an actionable way to lower that risk, too. Test your home for radon, especially if you live in a rural area or spend a lot of time indoors. If levels are high, professional mitigation can greatly reduce exposure—and potentially lower your long-term cancer risk.
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