“We’ve shown that the gene being changed is directly associated with asthma and severity of the asthma,” Dr. Kari Nadeau of Stanford University, the senior study author, told a press conference at the 2013 meeting of the AAAAI in San Antonio, Texas.

The new study shows that exposure to polycyclic aromatic hydrocarbons (PAHs) in the air directly led to a change in a gene known as FOXP3. This gene exists inside regulatory T-cells, whose job is to suppress inappropriate immune responses, such as the airway inflammation associated with asthma. This alteration in the gene makes it harder for the T-regulatory cells to do their job, leading to worsened asthma symptoms.

The study also associated PAH exposure with higher overall levels of IgE antibodies, which play a major role in any allergic response.

For the study, researchers observed a group of children and teens at two sites in California: Fresno, which is known for heavy air pollution and a high rate of asthma (about 22 percent), while Stanford, a lower-pollution area, was used as a control group. Measurements were taken of PAH levels in the air, the children were given lung function tests, and also gave blood and urine samples.

The children who had been exposed to PAHs for three months before the testing were more likely to have altered FOXP3 genes, decreased T-regulatory cell function and high levels of IgE antibodies. All three differences make asthma more likely, and its impact more severe.

“Exposure to high PAH quantities may be having an effect at the molecular level, possibly leading to new cases of asthma,” said Nadeau in a press release. This altered version of FOXP3 was even found in individuals from the area who didn’t have asthma – and it is unknown whether this change is reversible.

More than 100 chemicals are classified as PAHs, which form when an organic substance is burned incompletely. Sources include oil, gas, coal, tobacco, or even meat from a barbecue (when drippings fall onto the flames, PAHs are formed which then adhere to the meat). Man-made PAHs can also be found – in tars as well as some plastics, dyes and pesticides.

See Allergic Living‘s full coverage of the 2013 AAAAI allergists conference.

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