Sneezing already? Allergy season grows with warming weather in Minnesota.

Allergy season will soon be in full swing. But new research suggests many Minnesotans may already have runny noses and itchy, watery eyes — days or even weeks earlier than trees would typically release their pollen.

Climate Matters, a New Jersey-based environmental nonprofit, analyzed decades of federal weather data across nearly 200 U.S. cities, including Minneapolis, St. Paul, Duluth, Rochester and Mankato. The results, released earlier this month, show that in parts of Minnesota, the annual allergy season now lasts nearly a month longer on average than it did in the 1970s.

Minneapolis and St. Paul saw the biggest increase to their allergy season, with 27 extra days on average compared to 50 years ago. Duluth saw a 24-day increase over that period, and Mankato and Rochester added 11 and 10 days to their allergy seasons respectively.

The analysis adds to a growing body of studies that, for decades, have shown that seasonal allergies have worsened for people as the planet warms. Medical experts who specialize in allergies say that's because the warmer temperatures are triggering spring bloom earlier in the year, allowing plants to release their pollen for a longer time and even making the pollen itself more allergenic.

There's more carbon dioxide in the air, said Andrew Rorie, an allergy and immunology professor at the University of Nebraska and chair of the National Allergy Bureau. "So plants are happier and the growing days are longer throughout the course of the year."

Roughly one in four U.S. adults and nearly one in five children suffer from seasonal allergies, which are largely caused by tree pollen in the spring, grass pollen in the summer and weed pollen in the fall. The microscopic pollen particles stick to mucus membranes, causing inflammation and irritation to the nose and eyes. Some experience extreme reactions, including difficulty breathing.

Multiple peer-reviewed studies have tied warmer temperatures to longer pollen seasons, with many studies showing that plants are also producing more pollen than they did in the past. The research includes a 2016 study that found ragweed pollen season in Minnesota increased by up to 21 days on average between 1995 and 2015, as well as a 2014 study that found pollen season in the contiguous U.S. produced 46% more pollen on average between 2001 and 2010 compared to the previous decade.

"In the vast majority of locations, we're seeing a prolonged pollen season, to some degree, but also more pollen," Rorie said.

Not only is the pollen season being extended, but plants are also growing larger and releasing more pollen due to higher levels of carbon dioxide and ozone in the atmosphere, Rorie said. "In some instances," he added, "there's research showing that some of these pollutants are potentially making the pollen more allergenic."

Dr. John Moore, an allergist with M Health Fairview in Edina, sees that phenomenon among many of his patients.

"It seems like every year we have patients that are struggling to keep their allergies under control despite medications," said Moore, who has worked with allergy patients for 15 years in Minnesota and Iowa.

The same goes for Dr. John Sweet, medical director of Hennepin Healthcare's Allergy Clinic in Minneapolis.

"What I'm seeing in my patients is that a lot more are coming through on maximum dose of allergy medicines — oral antihistamines and steroid nasal sprays — but they're not getting relief," Sweet said. "We're having to prescribe even larger or higher-than-normal doses to reduce allergy symptoms."

For anyone struggling to find relief with over-the-counter medications, Sweet said, they should seek help from an allergist. There are also precautions Minnesotans can take to minimize their exposure to outdoor allergens, he added, such as regularly replacing filters in your air conditioning systems and showering before bed.

"Your hair acts like a giant pollen collector," he said. "The worst thing you can do is go back home, back to bed, with all that pollen in your hair."

Moore said allergy season typically starts in late March for Minnesota, but all the warm weather in recent weeks could prompt trees to bud early this year. In Madison, Wis., which is a little farther south than Minnesota, pollen counts already reached high levels last week, Moore noted.

Minnesota currently has no monitors for pollen levels, instead relying on stations in nearby states like Wisconsin and Iowa, as well as computer-modeled forecasts based on historic patterns. That means Minnesota's pollen levels are roughly estimated and may not always be accurate.

Moore said that can be a problem for his patients, who use resources, such as weather apps on their phone, to gauge pollen levels before going outside.

The Minnesota Department of Health was never given a mandate by lawmakers to collect pollen data and therefore has no funding for it, the agency said. And the state's previous pollen monitor, operated by a private research institute, was shut down in 2020 amid purported staffing issues during the pandemic and never brought back online. Data from that monitor shows that Minnesota's elevated pollen days have gone up since the 1990s

"It is unfortunate Minnesota doesn't have that," Moore said. "I definitely have patients who look to see what the pollen counts are before they choose to do certain things. You know, is this going to be my gardening day or not?"