Urban Light Pollution May Extend Allergy Seasons and Worsen Symptoms

City dwellers experiencing year-round allergy symptoms may have urban light pollution to blame. New research indicates that artificial nighttime lighting extends pollen production in plants, increases ragweed growth, and heightens human susceptibility to allergic reactions including sneezing and asthma.

The study, published in PNAS Nexus, examined the U.S. Northeast and found that urban trees begin producing pollen earlier in spring and continue later into fall compared to those in low-light areas. This extended period adds approximately 130 additional days of allergy exposure annually, researchers discovered.

Light pollution affects nearly 80% of North Americans who cannot see the Milky Way due to streetlights, car headlights, and illuminated billboards. This pervasive lighting alters the physiology of plants and humans alike, essentially “tricking plants into making decisions they wouldn’t ordinarily make,” according to Dr. Katz.

The research team used satellite nighttime light data and airborne pollen counts spanning over a decade. In cities like New York, allergy seasons often begin before March 1st, while darker areas like rural Connecticut see starts closer to April. New York’s season extends until early November, compared to October endings in darker regions.

Pollen counts in light-polluted areas are classified as severe about 27% of days during pollen season, versus 17% in darker areas. The urban heat island effect also contributes to extended growing seasons, but researchers found light pollution independently affects pollination timing.

Not all plants respond equally to lighting. Whilelime trees rely more on temperature, plane trees are highly sensitive to light and produce large amounts of allergenic pollen. These trees were widely planted in cities for their hardiness, despite their pollen issues.

Ragweed, which affects up to 20% of Americans, is particularly light-sensitive. Interestingly, its natural predator—earthworms—becomes inactive under streetlights, allowing ragweed to grow twice as tall in well-lit conditions.

Beyond plant interactions, artificial lighting may directly increase allergy risk by disrupting human circadian rhythms and triggering inflammation. A recent meta-analysis found light pollution correlates with 62% higher asthma risk and 89% higher allergic rhinitis risk, independent of air quality.

Solutions exist: cities can select less allergenic tree species, adjust streetlight brightness, and incorporate pollen data into forecasting systems to help people manage exposures and timing of medications.

1. Douglas Alteen

   Senior Editor

   I had allergies every spring as a kid. Sneezing, wheezing, the works. So editing this, my reaction was, “Ugh.” The good news is, there are things we can do.

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