Climate change triggers earlier mold allergy season, say Michigan scientists

• Fungal spore allergy season began 22 days earlier in 2022 than in 2003, a shift that researchers have linked to rising global temperatures causing fungi to release spores earlier in the year.
• Total spore counts fell during the same time period, likely due to drier conditions making it harder for spores to survive.
• Roughly 1 in 5 people showed sensitivity to mold allergens like spores, according to another 2023 study.

Seasonal allergies caused by mold and other fungi now start an average of three weeks earlier than 20 years ago nationwide, likely due to rising temperatures caused by climate change.

New research led by University of Michigan scientists and published in the journal GeoHealth found that fungal spore allergy season — when airborne spores give humans itchy eyes, stuffy noses and sneezes — arrived about 22 days earlier in 2022 than in 2003.

A monitoring station in St. Clair Shores observed the season creeping earlier by a few days each year, shifting the onset of the season from early July to mid-June over the course of the 20-year study period.

Some other places have it far worse.

In California, allergy season is getting earlier by roughly a week a year, shifting the season’s onset by nearly three months over the study period.

Some sites in the Great Plains saw their season start later, which researchers chalked up to wetter conditions in those areas.

Yiluan Song, a postdoctoral fellow at the Michigan Institute for Data and AI in Society who led the study, called the findings “a fingerprint of climate change.”

“We can use this as a way to communicate that climate change is impacting the ecological systems and call for actions to mitigate climate change,” Song said.

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While talk of seasonal allergies usually conjures images of golden pollen filling the air, causing runny noses and puffy eyes for allergy sufferers — fungal spores are also a significant driver of allergy symptoms.

They are microscopic particles that fungi release into the air to reproduce, a process triggered by rising temperatures in the spring and early summer.

A 2023 study found that roughly 1 in 5 people showed signs of sensitivity to fungal allergens like spores.

Across 55 monitoring stations scattered throughout the US, Song and her colleagues found a close relationship between rising temperatures and earlier spore seasons.

Mold allergy symptoms are similar to pollen allergy symptoms, including itchy and watery eyes, said Kathleen Slonager, the executive director of the Asthma and Allergy Foundation of America’s Michigan chapter. Prolonged exposure can cause asthma and aggravate asthma symptoms.

Past research has shown that pollen allergy season in Michigan is also beginning earlier and becoming more severe.

The findings are no surprise to allergists like Slonager, who has watched patients complain of earlier and more prolonged symptoms in recent years. 

“And now there is all kinds of data and research to support what allergy patients have been feeling,” she said.

Since most of the monitoring stations were positioned on urban rooftops, the data was mainly based on spores from outdoor fungi, Song said. But mold can thrive in dark and damp indoor places, too.

Song said people with mold allergies may want to start taking their medications earlier in the year and public health systems should also prepare for an earlier influx of allergy patients.

Decreased rainfall during the 20-year research window caused total spore counts to fall nationwide, which could suggest that some people’s allergies will be less severe than in the past, said Kai Zhu, a U-M associate professor of sustainability and environment and ecology and evolutionary biology who coauthored the study.

Rainfall this summer is expected to be average or “a tad” above normal, said Tom Kines, a senior meteorologist for AccuWeather.

But in the long run, scientists expect Michigan’s summers to get warmer and wetter due to climate change. 

Slonager, of the Asthma and Allergy Foundation, said the best way to avoid mold allergies is to limit outdoor activities when spore counts are high or use a dehumidifier to ward off indoor mold.

Medications like antihistamines or nasal corticosteroids can alleviate some symptoms, she said.

Researchers still haven’t determined how shifting allergy seasons might affect the environment, Song said.

Fungi play an important role in the ecosystem, helping decompose organic matter and releasing nutrients back into the soil for plants and other organisms.