Climate change and pollution are worsening your allergies

For millions of Americans, allergy season no longer follows the old calendar. Winters are shorter. Rising carbon dioxide levels are also helping plants produce more pollen.

More than one in four U.S. adults have seasonal allergies, according to the CDC, and for many, climate change is turning allergy season into a longer run of sneezing, congestion, and watery or itchy eyes.

Dr. Rebecca Saff sees the consequences in the clinic. Saff, an allergist and immunologist at Massachusetts General Hospital, said patterns have become harder to predict, especially in the northern United States. Patients who once had fairly distinct spring or fall symptoms are increasingly dealing with allergies for more of the year, and some are finding that medications that once kept symptoms under control no longer work as well.

In the conversation below, Saff explains how climate change, pollution, and milder winters are reshaping allergies and asthma, why mold and even some non-respiratory allergic conditions may be part of the story, and how patients can better prepare for a season that now often begins before it looks or feels like spring.

The nonprofit Climate Central recently found that the freeze-free growing season has lengthened in 173 of 198 American cities since 1970, by 21 days on average. How are shorter, milder winters changing what you see in the clinic?

In a few ways. Seasons are starting earlier, lasting longer, and becoming less distinct, so patients who once had predictable spring or fall symptoms are often struggling for more of the year.

We’re also seeing plants move northward – ragweed is a good example – so people in the Northeast are being exposed to allergens that used to be less common here. That means more patients are reacting to more plant species, for longer. Even people with historically mild seasonal allergies are noticing sharper symptom peaks, and medications that once kept things under control are not working as well as they once did.

How do shorter winters affect insect-related health risks?

We see more venom allergies and more mosquito-borne illnesses because we don’t get as many hard freezes as we used to. We have more mosquitoes for longer stretches of the year, and more ticks for longer as well.

Urban areas are warmer and tend to be more polluted than rural areas. Do you see differences in allergen symptoms?

Rising carbon dioxide [CO2] levels change the way plants produce pollen, and urban areas tend to have higher CO2 concentrations. Both plant biomass and pollen concentrations increase as CO2 levels rise.

There was a study in Baltimore that looked at ragweed. It compared urban areas of Baltimore, where CO2 levels were higher, to areas just outside the city. The urban plants had greater biomass and produced more pollen per plant.

Urban residents are more likely to experience pollution and pollen at the same time. How does that change what allergies look like in the clinic – especially for people with asthma or other respiratory problems?

There are a couple of ways. Air pollutants can increase inflammation in the sinuses, nasal cavity, and respiratory tract. That can make people more susceptible to allergen-induced inflammation because they are already chronically inflamed; it makes symptoms worse. Studies have also shown higher ER visit rates among patients with asthma when air pollution levels are higher. Pollutants clearly affect respiratory health overall.

More extreme weather events – including hurricanes and heavy rains – lead to flooding and mold. After Hurricane Sandy and Hurricane Harvey, studies showed higher mold levels in affected areas and increased respiratory disease

If the old allergy calendar is becoming less reliable with climate change, what should patients, doctors, schools and public health officials be doing differently now?

Even in March, when there’s still snow on the ground here in Massachusetts, we’re telling patients to start their allergy medications. We know it helps to begin treatment before pollen counts rise, so people can stay ahead of symptoms. That used to mean starting in mid-April. Now we’re asking patients to begin in mid-March.

Good data are also important. I’m a member of the American Academy of Allergy, Asthma & Immunology, which runs the National Allergy Bureau. Its pollen and mold data come from counting stations around the country; it’s a reliable source. A lot of mainstream weather apps don’t explain where their pollen data come from and their data aren’t always as accurate as you’d expect. We encourage patients to use reliable data to prepare and protect themselves.

What are some of the newer avenues of research in this field?

We tend to think about pollen mainly in terms of seasonal allergies and asthma, but the effects may be broader. There’s growing evidence that higher pollen levels can also affect conditions like eosinophilic esophagitis – an allergic inflammation of the esophagus – and even eczema. So this is not just about the respiratory tract. Environmental exposures may be influencing allergic disease more broadly than we once thought.

-As told to David Trilling