High Levels of Prenatal PFAS Exposure May Increase Risk of Childhood Asthma

Children whose mothers are exposed to very high levels of per- and polyfluoroalkyl substances (PFAS) have a significantly higher risk of developing asthma, a new study has found.

The study, which examined data relating to more than 11,000 children born in the Swedish county of Blekinge, also found no increase in asthma incidence among children whose mothers were only exposed to intermediate or low levels of PFAS during their pregnancies.

Based on these findings, the researchers believe it is important to research whether similar trends are seen in other areas and populations with very high PFAS levels to clarify how exposure might affect childhood lung function and development.

Asthma and PFAS: What do we know so far?

Previous research into PFAS and asthma in young children has yielded mixed results; one notable recent study of data from more than 600 children aged 3–11 years concluded that there was “some evidence” that PFAS concentrations in blood serum were “weakly associated with increased asthma prevalence.”

“While there has been some experimental evidence linking PFAS exposure to changes in lung function, results from previous epidemiological studies in humans were quite mixed—some studies found an association between PFAS and asthma, but many did not,” study author Annelise J. Blomberg, ScD, associate researcher at Lund University, told Technology Networks.

However, Blomberg pointed out that most previous studies looked at populations with low overall PFAS exposure. “Our study investigated effects in a population that included children who had been exposed at very high levels from PFAS contamination in their drinking water,” she said.

The origin of this very high exposure comes from the drinking water in Ronneby municipality in Blekinge, where in 2013 it was discovered that nearby fire drills had contaminated the town’s drinking water supply with PFAS-containing firefighting foams. Locals had been exposed to this contamination for over 30 years, meaning that many couples had children without knowing that their child was being exposed to PFAS in utero. PFAS have previously been shown to be able to cross the placental barrier, raising concerns about the health effects of prenatal PFAS exposure.

Another limitation on studying the associations between PFAS exposure and asthma, in particular, is that asthma can be difficult to diagnose in very young children. Since these children cannot reliably complete standard lung function tests, such as spirometry, diagnosis often hinges on observing wheezing and similar symptoms. However, wheezing is also commonly seen in viral infections, and many children have episodes of transient wheezing—something that they will grow out of without ever developing asthma.

“To account for this, we also included a stricter asthma definition that only included children who met the diagnosis criteria after age 36 months—when it becomes easier to make an asthma diagnosis,” Blomberg said. The study also included broader outcome measures, which included early-life (before 36 months) wheezing, asthma diagnoses, and asthma-related drug dispensations.

Only very-high PFAS exposure levels linked to childhood asthma

The study looked at population and health registry data from all children born in Blekinge county between 2006 and 2013—the 7-year span before Ronneby’s high PFAS levels were discovered. This included clinical diagnosis data from doctor and specialist visits, as well as data on drug prescriptions dispensed by pharmacies.

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Prenatal PFAS exposure was estimated using the mother’s residential address during the five years before the baby’s birth. Children were categorized as being at “very high” exposure if their mother lived at a Ronneby address affected by the contaminated water for the five years preceding birth. “High” exposure was defined as the mother living at such an address for at least one year, “intermediate” was used if she lived in Ronneby but not at an affected address, and exposure was identified as “background” if she lived elsewhere in Blekinge county.

“We saw a strong link between PFAS and childhood asthma, but only in children who had been highly exposed to PFAS from contaminated drinking water at levels hundreds of times higher than the general population,” Blomberg said. “We did not see an association at intermediate levels of exposure.”

“The association between PFAS and this ‘more strict’ asthma diagnosis was actually stronger than in our primary asthma definition,” she added.

Overall, very high prenatal PFAS exposure was associated with approximately a 40% increase in the risk of developing asthma.

The paper speculates as to the biological mechanisms that may explain a relationship between PFAS exposure and asthma; prenatal exposure to perfluorooctanesulfonic acid (PFOS), a type of PFAS, has been shown to inhibit perinatal lung development and induce oxidative injury in rat studies, with in vitro studies also indicating that PFAS exposure can aggravate mast cell-mediated allergic inflammation.

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However, the researchers are clear in stating that this new study cannot prove any causal link between prenatal PFAS exposure and asthma cases, due to its observational nature.

“Our exposure measure was based on residential address rather than individual biomarker measurements, and we also could not fully separate prenatal from early-life exposure effects,” said Blomberg, explaining the study’s limitations. “Finally, this is an observational study using real-world data. While we tried to account for other factors that might impact asthma, we can't rule out other explanations, and we can't say for sure that the high PFAS caused asthma.”

“The most important next step is to replicate this study and see whether similar results are observed in other high-exposure populations. Beyond this, we hope to investigate how PFAS impacts lung function more generally, and whether any effects are detectable at lower exposure levels.”

Reference: Blomberg AJ, Nielsen C, Bolmsjö BB, Bind MA, Hartman L, Jöud AS. Prenatal exposure to per- and polyfluoroalkyl substances (PFAS) and incidence of asthma and wheeze in childhood: A register-based cohort study in Ronneby, Sweden. PLOS Medicine. 2026;23(4):e1004659. doi: 10.1371/journal.pmed.1004659

About the interviewee:

Annelise J. Blomberg, ScD, is an associate researcher at Lund University's Faculty of Medicine. As an environmental exposure scientist and epidemiologist, Dr. Blomberg characterizes human exposures to environmental contaminants and examines how these exposures impact health. Her current research focuses specifically on the health effects of early-life exposures to perfluoroalkyl substances (PFAS) at both low and high levels. Prior to joining Lund University, Dr. Blomberg completed her doctorate and a postdoctorate fellowship at Harvard T.H. Chan School of Public Health.