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Allergy symptoms got you down? Blame pollen AND air pollution. » Yale Climate Connections


You are not alone if every pollen season feels worse than the year before.

Pollen season is starting earlier and lasting longer, and even those previously unaffected are noticing its impacts. Across the globe, allergic reactions to pollen have increased in frequency and severity over the last several decades.

The evidence is clear to the naked eye: the dusting of yellow-green powder on outdoor patio furniture and cars parked on the street and the itchy eyes, runny noses, and sleepless nights starting weeks earlier than in the past.

“What we know right now is across the U.S., climate change is making pollen seasons longer and pollen concentrations higher. And that’s true for grasses, weeds, and trees,” says Nicholas Nassikas, a pulmonologist and researcher at Beth Israel Deaconess Medical Center. 

Warmer temperatures lead to earlier springs and more pollen. Higher carbon dioxide levels in the atmosphere, one of the biggest drivers of climate change, can also make pollen more potent and, therefore, more allergenic — in other words, more likely to cause symptoms.

Recently, another piece of the puzzle has received more attention: the interaction between pollen and air pollution.

Research shows that the irritant we are used to blaming for our seasonal misery — pollen — is only part of the problem. Pollutants from sources like cars and factories, particularly concerning to people living in urban areas, can also intensify our allergic reactions.

In a complex interplay, pollen and pollution can worsen allergies and long-term health risks from conditions like asthma. On the flip side, taking action to limit local pollution may be one way communities can help reduce allergy symptoms during pollen season. Read on for more on the science behind the increasing risk and what you can do about it.

Air pollution, plant stress, and ‘polluted pollen’ 

Most people recognize that air pollution — a mix of hazardous gases and particulate matter — harms human health and the environment. Air pollutants can cause or aggravate lung diseases and heart disease and even affect cognitive function.

Less well-known is pollution’s invisible toll on plant life.

“Plants that are grown in pollution-stressed situations are known to release more allergens,” says Elaine Fuertes, a research fellow at the National Heart and Lung Institute, Imperial College London.

Depending on the plant species, air pollutants can change the chemical composition of pollen, increasing the potency of pollen allergens and triggering stronger allergic reactions in people.

When researchers in Spain compared grass pollen from polluted urban zones to less polluted rural zones, people exposed to “polluted pollen” showed more skin reactivity, indicating a stronger allergic reaction, during allergy testing. These results echo findings from another study where pollen from pine trees with the highest exposure to the air pollutant ozone showed higher levels of allergenicity in participants.

Air pollutants like particulate matter and nitrogen oxides may also make the exine — the outer coating of pollen grains — from some plant species more fragile and, therefore, more likely to rupture into smaller fragments that can penetrate deeper into the lungs.

This revelation may help explain why people often experience troublesome allergy symptoms even on days with low pollen counts.

“Each pollen grain releases a different amount of allergen in the air. This idea that just measuring a pollen count will be a one-to-one relationship with the actual amount of allergens has been essentially shown to be false,” Fuertes says.

Fuertes says pollen counts are still important, but we are likely measuring the wrong marker if we want to improve forecasting and provide patients with the most useful piece of information about day-to-day allergy risk.

“Our group is trying to push the measurement of allergen levels because this relationship between pollen counts and allergen levels is influenced by climate but also pollution,” she says.

She points to recent work showing that a new test for grass allergen levels connected more consistently with people’s experience of allergy symptoms than grass pollen counts. But researchers’ ability to measure allergen levels for the vast array of plant species is still in the experimental stages.

Double whammy: Air pollution weakens human defenses to pollen 

It gets worse: Air pollution causes harm beyond changing the potency of plant pollen.

When people breathe in pollutants like ozone, particulate matter, and diesel exhaust particles, these toxic exposures damage the lining of our airways and interfere with our body’s defenses in ways that can amplify our reactions to pollen.

“The air pollution is making the pollen more potent. And the exposure of each of them at the same time is priming the lungs to have almost a more exaggerated response,” says Nassikas, the pulmonologist.

Usually, a thin layer of protective mucus and small hairlike projections on the surface of the cells that line our nasal passages and lungs help capture and clear inhaled particles like pollen. However, exposure to air pollution can weaken this defense system, allowing allergens to stick around longer and penetrate deeper into our tissues, making it easier for pollen to trigger an allergic response.

And air pollution can prime us to develop pollen allergies in even more insidious ways.

Our immune systems develop over time, responding to everything in the environment — from the food we eat to the air we breathe. Exposure to a range of germs and chemicals in the environment helps the immune system learn what is dangerous and needs to be removed from the body and what is harmless and can be ignored. When our immune system is exposed to air pollutants like particulate matter, it can become dysregulated — and start to attack harmless substances like pollen.

Researchers have found that diesel exhaust particles, commonly found in traffic pollution, can increase immunoglobulin E (IgE) levels, a key player in allergic reactions. In another study focused on people sensitive to ragweed pollen, individuals exposed to both diesel exhaust particles and ragweed pollen allergens had an allergen-specific IgE response 16 times higher than when exposed to the pollen allergen alone.

More research is needed to fully understand the impacts of the combination of air pollution and pollen, but there is strong experimental evidence that exposure to both can worsen health.

“The interaction between air pollutants and pollen not only affects immediate allergic reactions but also contributes to long-term respiratory issues,” Fuertes says.

The problem is set to get worse as the climate changes

As global temperatures rise, longer and more intense pollen seasons are expected, alongside worsening air quality from air pollutants like ground-level ozone. This means that seasonal allergies and other allergic lung diseases like asthma will likely continue to increase — and current research about the health and quality of life impacts of allergies is just catching up.

“We’re really at the tip of this iceberg looking at only the severe cases … We are missing a huge chunk of the burden,” Fuertes says.

How to protect yourself from pollen and air pollution

As a pulmonologist, Nassikas often recommends various interventions to protect his patients from air pollution and pollen. His advice:

  • Monitor air quality and pollen counts: Stay informed about air quality indexes and pollen forecasts. This knowledge can help you plan outdoor activities to avoid peak pollution and pollen exposure times.
  • Improve indoor air quality: Consider air purifiers with HEPA filters to remove pollen, pollutants, and other allergens from indoor air. Keep windows closed during high pollen days to prevent these irritants from entering homes and workplaces.
  • Treat and manage symptoms: An array of management strategies can potentially help control allergies, from nasal saline washes, antihistamines, and intranasal corticosteroids to immunotherapy. Your health care provider can help you understand the best options.
  • Be a clean air advocate: The battle against seasonal allergies is not just about steering clear of pollen and managing symptoms. It’s also about addressing air quality. You can take part in your community by using public transportation, biking and walking whenever possible, investing in an electric vehicle, or supporting clean energy initiatives.

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