For New Yorkers who feel like allergy season never really ends, the culprit might not just be the trees but the lights shining on them. A new regional study finds that artificial light at night is stretching pollen seasons in bright Eastern cities, leaving residents in places like New York and Philadelphia with more days of high pollen and more intense allergy exposure. Researchers say all that extra glow at night can reset plants’ internal clocks, so they start and stop releasing pollen on a very different schedule than their rural counterparts.
The findings come from a PNAS Nexus paper that paired daily pollen records from 12 National Allergy Bureau stations with satellite maps of nighttime light across the Northeastern United States from 2012 through 2023. The authors report that areas with higher artificial light at night (ALAN) tended to see pollen seasons begin roughly 20 days earlier and end weeks later, often stretching beyond 200 days even after accounting for temperature and rainfall, according to PNAS Nexus. The study also found that ALAN-exposed locations logged a higher share of "severe" pollen days, suggesting a measurable public health burden for people living under the brightest skies.
A write-up that uses NASA’s Black Marble night-light imagery drives home just how stark the bright-versus-dim divide can be: low-light areas typically saw significant pollen about 170 to 210 days a year, while some brightly lit urban centers, New York among them, recorded as many as 300 pollen days annually. The NASA piece notes that severe-exposure days made up about 27% of the season in ALAN-heavy areas, compared with around 17% where outdoor lighting is minimal, and it highlights practical fixes like shielding fixtures, using motion sensors and cutting back on blue-rich LEDs. Taken together, those numbers suggest that a city’s lightscape can directly shape how long, and how intensely, residents are breathing in airborne allergens, according to NASA.
What Researchers Are Saying
Daniel Katz, a co-author of the study and a plant scientist, told The New York Times that "we’ve basically tricked plants into making decisions they wouldn’t ordinarily make," pointing to how plants use daylength as a cue for when to flower and release pollen. As Marta Zaraska reports in the Times, the study’s technical results track with real-world spikes in urban pollen and add to a growing list of ways city living can quietly reshape health risks for residents.
What You Can Do
If spring and fall already have you stockpiling tissues, the personal playbook stays familiar: monitor daily pollen counts, cut back outdoor time on high-pollen days when you can, and keep allergy medications and inhalers up to date. The National Allergy Bureau, whose stations supplied the pollen data for the study, posts local daily counts and maps that can help people plan their days, according to AAAAI's NAB. On a broader scale, the study’s authors and NASA scientists point to municipal fixes such as better shielding on streetlights, dimmer and warmer bulbs, and smarter timers that reduce plants’ exposure to nighttime light and could be folded into public health planning, according to PNAS Nexus.
Light pollution has already transformed the night sky for most people: atlas work shows that roughly 80% of North Americans can no longer reliably see the Milky Way from home, a reminder that darkness itself has become rare, according to National Geographic. The new PNAS Nexus results tack on a very down-to-earth consequence to that fading night. Where the sky stays bright, allergy seasons may be getting longer, harsher and more likely to keep New Yorkers reaching for tissues and inhalers well beyond the traditional spring sneeze window.
