Radon and Ovarian Cancer Risk: What a 2026 JAMA Study Means for Pennsylvania Homeowners

What the 2026 JAMA Network Open Study Found

Researchers from the Women's Health Initiative (WHI) published findings in April 2026 examining whether where a woman lives — specifically, the radon potential of her county — correlates with her risk of developing or dying from ovarian cancer. The study, authored by Williamson, Whitsel, Smith, and colleagues, is the first epidemiologic investigation of its kind.

Study design and cohort. The analysis drew on data from 127,547 postmenopausal women enrolled at 40 clinical centers across the United States between 1993 and 1998. Participants were followed through 2024, yielding a follow-up period of approximately 31 years. At enrollment, each woman's home address was geocoded and matched to 1993 USGS radon zone data, providing a geographic proxy for long-term residential radon exposure.

Radon zone classification. The USGS system divides counties into three zones based on predicted average indoor radon levels. The study used this same framework: Zone 1 counties predict indoor radon above 4 pCi/L (high), Zone 2 counties predict 2–4 pCi/L (medium), and Zone 3 counties predict below 2 pCi/L (low). The low zone served as the reference group for all hazard ratio calculations.

Outcomes. Over the follow-up period, 1,645 incident ovarian cancers were recorded, along with 1,048 ovarian cancer deaths. Both incidence and mortality were analyzed against radon zone assignment.

Primary findings. For all ovarian cancer types combined, women living in high-radon counties (Zone 1) had a hazard ratio of 1.31 (95% CI, 1.11–1.54) compared to women in low-radon counties — a statistically significant 31% higher rate. The medium-zone result (HR 1.13; 95% CI, 1.00–1.29) was not statistically significant, suggesting the elevated risk is concentrated in the highest exposure category. For ovarian cancer mortality, the hazard ratio for high versus low zones was 1.31 (95% CI, 1.07–1.60), consistent with the incidence findings.

Serous subtype. Serous ovarian cancer — the most common and lethal histologic subtype — showed the strongest association. Women in high-radon zones had a hazard ratio of 1.38 (95% CI, 1.09–1.74) for serous ovarian cancer specifically, suggesting that if a biological mechanism exists, it may be particularly relevant to this subtype.

The authors describe radon as both ubiquitous and modifiable — a combination they note makes it a meaningful target for public health intervention even in the absence of established causation.

Why This Matters Specifically for Pennsylvania

The study's exposure classification maps directly onto Pennsylvania's documented radon landscape. The threshold separating high from low exposure — 4 pCi/L — is identical to the EPA's residential action level and to the boundary between USGS Zone 1 and Zone 2.

Pennsylvania's Zone 1 footprint is unusually large. Thirty-seven of Pennsylvania's 67 counties are classified as USGS Zone 1 — the highest proportion of any state in the country. Approximately 40% of tested Pennsylvania homes exceed the 4 pCi/L threshold. For context, the national average is roughly 8%.

The Reading Prong is the primary driver. Pennsylvania's southeastern and south-central counties sit atop the Reading Prong, a geological formation of Precambrian granitic gneiss containing elevated concentrations of uranium-bearing accessory minerals. This rock produces the highest indoor radon concentrations in the eastern United States. The uranium decays to radium, which decays to radon-222, which migrates through thin soil mantles and fractured bedrock into building foundations.

Pennsylvania's DEP references USGS zone data in its public radon guidance, and the 2026 JAMA study's use of the same USGS framework means its findings are directly applicable to Pennsylvania homeowners without any geographic translation.

Geographic Zone Data vs. Your Actual Home

An important limitation of the JAMA study — one the authors themselves acknowledge as primary — is that USGS zone assignments are population-level predictions, not individual home measurements.

A home in Berks County (Zone 1) can test below 2 pCi/L depending on its foundation type, soil permeability beneath the slab, construction vintage, and ventilation characteristics. A home in a Zone 2 county can test above 8 pCi/L if it happens to sit over a fractured bedrock pathway or a karst void. The study enrolled women in 1993 and used that year's address to assign radon zone — there is no way to know what each woman's actual home radon level was, or whether it changed over decades of follow-up.

This geographic proxy approach is standard in large epidemiologic cohort studies where individual exposure measurement is impractical. But it means the study identifies an association between residing in a high-radon county and increased ovarian cancer risk — not necessarily between any specific measured radon concentration and individual cancer risk.

The practical implication: your county's zone classification gives you a baseline expectation, but it does not tell you what is actually in your home. A certified radon test is the only way to know your actual exposure.

Mitigation as a Modifiable Risk Factor

The study authors describe radon as ubiquitous and modifiable, situating it in the category of environmental risk factors that are actionable even without confirmed causation. This framing aligns with EPA's longstanding public health position: the evidence is sufficient to warrant action above 4 pCi/L regardless of whether every mechanistic pathway has been fully characterized.

Sub-slab depressurization (ASD). The EPA-recommended mitigation system for homes testing above 4 pCi/L involves installing a pipe through the slab and a fan to draw radon-bearing soil gas from beneath the foundation and vent it above the roofline — bypassing the building envelope entirely. Post-mitigation testing under ANSI/AARST MA-SAMP standards confirms system effectiveness. Properly installed ASD systems typically reduce indoor radon by 80–99%.

Pennsylvania certification requirements. Under PA Code Title 25, Chapter 240, radon mitigation contractors in Pennsylvania must hold DEP certification. This is not a voluntary credential — it is a legal requirement for commercial radon mitigation work in the state. Homeowners should verify contractor certification through the PA DEP before hiring.

Study Limitations

The JAMA Network Open findings warrant careful interpretation alongside their limitations:

Observational design. The study identifies a statistical association between county-level radon zone and ovarian cancer outcomes. It does not establish that radon causes ovarian cancer. Residual confounding — the influence of unmeasured factors that correlate with both radon zone and cancer risk — cannot be ruled out in an observational study of this design.

Geographic proxy, not measured exposure. The use of USGS zone data rather than measured indoor radon is the most significant methodological limitation the authors identify. Zone assignment reflects expected county-level averages, not the actual radon concentrations experienced by individual women over decades.

No remediation data. The study has no information on whether participants mitigated their homes during the follow-up period. Women who reduced their radon exposure after enrollment would be misclassified as high-exposure throughout, potentially diluting any observed association toward the null.

Residential mobility. Participants were assigned a radon zone based on their 1993 enrollment address. Women who moved to counties with different radon profiles during the 31-year follow-up would carry an incorrect exposure label.

Population scope. The cohort consists entirely of postmenopausal women aged 50–79 at enrollment. The findings cannot be directly extrapolated to younger women or men, nor to exposure patterns that differ substantially from the U.S. residential environment of the 1990s and 2000s.

First study of its kind. The authors emphasize that this is the first epidemiologic study of residential radon and ovarian cancer. Replication in independent cohorts — ideally with measured indoor radon rather than zone proxies — is needed before population-level public health conclusions can be drawn.

Frequently Asked Questions

Does radon cause ovarian cancer?

A 2026 study in JAMA Network Open found an association between living in high-radon areas and increased ovarian cancer risk in postmenopausal women, with a hazard ratio of 1.31 compared to low-radon areas. The study does not establish causation. It is the first epidemiologic study of radon and ovarian cancer.

What radon level was associated with higher ovarian cancer risk in the JAMA study?

The study classified high radon exposure as living in a USGS zone predicting indoor levels above 4 picocuries per liter (pCi/L) — identical to the EPA residential action level.

Which Pennsylvania counties have the highest predicted radon levels?

Counties within Pennsylvania's Reading Prong geological formation — including Berks, Montgomery, Northampton, Bucks, Chester, Lancaster, and Lebanon counties — are classified as USGS Zone 1, predicting average indoor radon above 4 pCi/L.

What type of ovarian cancer showed the strongest association with radon?

Serous ovarian cancer showed the strongest association, with a hazard ratio of 1.38 (95% CI, 1.09–1.74) for women in high-radon zones versus low-radon zones.

How can Pennsylvania homeowners reduce radon exposure?

The EPA recommends sub-slab depressurization (ASD) systems installed by certified professionals for homes testing above 4 pCi/L. In Pennsylvania, mitigation contractors must hold DEP certification under PA Code Title 25, Chapter 240.