A new scientific study has found that allergy season caused by fungal spores is starting much earlier than it did two decades ago. The research, published in the journal GeoHealth and led by the University of Michigan, shows that fungal spore seasons in the United States now begin on average 22 days earlier than in 2003.

“This is the first time that we’ve been able to show that the fungal spore seasons have changed, and the change is pretty big. That’s three weeks over the past two decades,” said Professor Kai Zhu, one of the senior authors of the study.

Fungal spores are tiny particles released by mold and other fungi to reproduce. They are so small that they easily float in the air and can enter our lungs without us noticing. Like pollen, these spores can trigger allergic reactions—sneezing, runny nose, itchy eyes, and in some cases, serious breathing problems such as asthma attacks.

In a 2023 study analyzing health records from over 1.6 million patients in the U.S., about 1 in 5 people showed signs of being sensitive to fungal allergens. This means millions are vulnerable to the health effects of these spores, especially when they arrive earlier than expected.

The team analyzed data from 55 monitoring stations part of the U.S. National Allergy Bureau, covering 2003 to 2022. These stations count both pollen and fungal spores in the air.

“Over the past two decades, fungal spore seasons in the U.S. have shifted significantly due to climate change. This has implications for both ecosystem processes and human health,” said Ruoyu Wu, who led the project during her master’s studies.

They found not only that the season for allergic reactions is starting earlier, but also that fungal reproductive cycles in nature are shifting by about 11 days on average.

The researchers say that rising temperatures are pushing fungal spore seasons to start earlier in the year. At the same time, drought in many regions may be reducing overall spore production. This complex balance means we have a longer allergy season but, paradoxically, potentially fewer total spores being produced.

Doctors advise that people who suffer from mold allergies may need to begin taking treatments or precautions earlier in the year.

Buildings themselves can also be a source of spores. “We also know that buildings and vegetation are huge sources of fungal spores in the air,” said Dr. Yiluan Song, another author of the study. This makes mold control in homes, schools, and offices an important part of allergy prevention.

Fungi are vital in nature—they decompose dead plants and animals, returning nutrients to the soil. Changes in their reproductive cycles may disturb ecosystems and food webs.

Dr. Song stressed the connection between climate change and these shifts: “Here, we see a very visible fingerprint of climate change. So another key action item is to try to curb climate change.”

This research underscores how climate change is not just about rising sea levels or hotter summers, but also about subtle changes that affect human health and the environment in ways we’re only beginning to understand.