Houston pollen, mold counts have spiked. Here's one reason why

A honey bee searches for pollen on a native Texas frostweed plant in the yard of Texas-certified native landscaper Doreen Gallevo on Oct. 1 in Houston.

New data from the Baylor College of Medicine suggests that rapidly increasing pollen counts are making Houston an even more challenging place for allergy sufferers to call home.

Sanjiv Sur, professor of medicine and the director of allergy and immunology at Baylor, discovered this startling spike by analyzing daily data published by the Houston Health Department.

FALL ALLERGIES: The most common fall allergens are in full bloom currently. What other allergens could be causing you to sneeze?

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“What we found is that there has pretty much been a doubling of mold counts in 10 years and there’s been a huge increase in cedar elm tree pollen,” Sur said, adding that the increased numbers are likely not the result of any sort of small environmental changes.

“It’s well known that pollination depends heavily on weather patterns and altitude,” Sur said. The increase in pollen counts, especially in the short span of only 10 years, leads Sur to believe a warming climate is at least partially to blame. “I would think such major rises in numbers should take 50 to 100 years, not 10 years,” Sur said.

“What we’re seeing is ragweed is pollinating at the same time as cedar elm, so the amount of pollen we’re being exposed to has greatly increased during the fall,” Sur said.

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These increases have led to what would be considered months of heavy to extremely heavy pollen counts. Ragweed pollen, a common fall allergen, has increased by a total of 1,900 grains of pollen per cubic meter of air, while elm and cedar elm have increased by about 8,500 grains of pollen per cubic meter of air.

Houston’s warm and humid climate is also a breeding ground for mold spores. Sur noted that as Houston’s climate becomes increasingly warm and humid, mold spores can proliferate much longer than they once could. Mold spores in the Houston metro area used to primarily crop up in the warm and wet summer months. Mold spores have been thriving deeper into fall over the past 10 years, and could do so again this year as a result of the wet spring and heavy rainfall from Hurricane Beryl.

“Freezes don’t occur until the end of fall in Houston, so that means allergens can thrive in this environment before the first freeze comes in,” Sur said. Freezing temperatures, which could come later than normal this winter, thanks to La Niña, are what provide the Houston metro area with some relief from allergen-producing pollen and mold.

Oak trees line the trail along Rice Boulevard in this photo taken in April 2022, near Rice University in Houston. The air in the area is prone to having high levels of airborne pollen.

None of this comes as good news for people sniffling and sneezing with seasonal allergies, a number that accounts for nearly 25% of the U.S. population, according to data from the national Centers for Disease Control and Prevention.

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The population of allergy sufferers may go up as more people flock to Southeast Texas from other regions of the country.

“As the population increases locally, the number of people being exposed to local allergens is also increasing, and it can take three to five years to become desensitized,” Sur said. Houston’s metropolitan population increased to more than 7.5 million people in 2023 alone, an increase of nearly 2% compared to 2022.

Are Houston residents who don’t suffer from seasonal allergies at risk for developing them soon, as pollen counts rise in a warming climate? That’s the million-dollar question.

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“At this time, all we know for certain is that there’s been a huge increase in mold and pollen counts, but I do suspect that at some point the number of people with allergies will go up,” Sur said, adding that this increase will take some time to notice.

Houston Health Department Microbiologist Christina Utz studies pollen and mold from a spore sample last year in March at the department's lab in Houston.

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