Per- and polyfluoroalkyl substances (PFAS) are widely used chemicals that persist in the environment because they have a long elimination half-life. Children can be exposed to PFAS, which are known as "forever chemicals," even before birth because these chemicals cross the placenta and are transferred into breast milk.

Studies have found that PFAS exposure can affect the immune system and may play a role in the development of asthma.

When researchers at Lund University in Sweden studied the health outcomes of kids living in an area with especially high levels of exposure, they found there was a strong association between prenatal PFAS exposure and childhood asthma.

PFAS or per- and polyfluoroalkyl substances cross the placenta and are transferred into breast milk, so infants are exposed before birth and while nursing.

The study looked at a group of residents in the city of Ronneby in Blekinge County, Sweden. They had been exposed to PFAS for more than three decades when their drinking water became contaminated with aqueous film-forming foam.

The water contamination in Ronneby led to PFAS exposure levels hundreds of times higher than the general population, allowing researchers to evaluate the health effects of exposure across a much wider range than previously.

The researchers concluded that asthma is a significant and previously under-recognized public health consequence of PFAS contamination. “Our findings suggest that very high prenatal PFAS exposure may have lasting consequences for children's respiratory health,” the researchers said.

They analyzed data from almost 11,500 children born in Blekinge County, including the city of Ronneby, between 2006 and 2013. Maternal addresses during the study period were linked to water distribution records and data from the National Patient Register to estimate prenatal PFAS exposure levels.

The children were followed from before birth until they were 12 years old or until December 31, 2022 and were grouped according to their level of prenatal PFAS exposure: two percent were in the very high exposure group, four percent were in the high exposure group, 14 percent were in the intermediate exposure group and 80 percent were in the background, low-level exposure group.

The water contamination in Ronneby, Sweden led to PFAS exposure levels hundreds of times higher than the general population and revealed a connection to higher rates of asthma.

Data from the patient register were also used to track asthma diagnoses and prescriptions.

During the follow-up period, 17 percent of the children were diagnosed with asthma. Almost 27 percent of those in the very high exposure group were diagnosed with asthma compared to 16 percent of those in the background exposure group, even after adjustment for family and socioeconomic factors.

Further studies replicating these findings in other populations that have been exposed to high levels of PFAS are needed to add support to the association between high levels of prenatal exposure and asthma.

The study was published in PLOS Medicine.