The Natural Resources Defense Council (NRDC) released a new report that might explain why some allergy sufferers have been having a more miserable time than usual: climate change.

NRDC cited prior studies have shown climate change “could favor the formation of more ozone smog in some areas;” this increases the production of ragweed pollen. The two together worsen respiratory health, triggering asthma attacks and even worse allergy symptoms. So the NRDC set out to update its map of the more vulnerable cities in the U.S.; it's among the first to curate a map at all, Live Science reported.

Researchers analyzed ozone data collected by the U.S. Environmental Protection Agency website from 2009-2013, as well as the counties the USDA Natural Resources Conversation Service PLANTS confirmed to have ragweed presence. Granted, ragweed pollen isn’t the only driver of seasonal allergies — but the NRDC cited pollen in particular has a well-known association with allergy rhinitis. The results showed the cities where climate change and pollen have a higher rate of intersection are:

Richmond, Va.
Memphis, Tenn.
Oklahoma City
Chattanooga, Tenn.
New Haven, Conn.
Allentown, Pa.

"Millions of us are sneezing and wheezing from allergies and asthma worsened by climate-change-fueled ragweed pollen and ozone-smog pollution," Juan Declet-Barreto, a fellow in the climate and clean air program at NRDC, told Live Science. "This double-whammy health threat will only intensify, and affect more people if we don't take steps to reduce climate change now.”

Ozone smog and pollen each individually complicate a person’s health: Ozone smog is an irritant that inflames the lungs, leading to increased respiratory problems, while pollen contains proteins that can trigger allergic reactions. The two start to intertwine when industrial facilities, electric power plants, and motor vehicles release ozone-producing chemicals into the air, the NRDC reported. These chemicals emit the carbon pollution responsible for climate change.

“Minimizing emissions from these sources can help reduce ozone air pollution and climate change, helping to create better air quality conditions today and a cooler, healthier environment in the future,” the report concludes.

One in three Americans, or 109 million people, is living in these allergy and asthma capitals in the U.S. To avoid overexposure, the NRDC suggests keeping track of local pollen counts, using air conditioners to recirculate air, and toweling off or taking a shower after working or playing outdoors.

For more seasonal allergy relief, click here.

Source: Declet-Barreto J and Alcorn, S. Sneezing and Wheezing: How Climate Change Could Increase Ragweed Allergies, Air Pollution, and Asthma. NRDC Report. 2015.