Plants don't sleep under streetlights and office building glow. New research shows they're confused by it — and that confusion is making allergy season longer and worse for millions of people.
Ecologists have long known that artificial light at night disrupts wildlife. Migrating birds crash into lit buildings. Sea turtles lose their way. But a study spanning 2012 to 2023 reveals a quieter problem: plants exposed to nighttime artificial light produce pollen for an extended period, stretching allergy seasons by roughly one to two weeks across northeastern US cities like New York, Boston, and Philadelphia.
"If you're someone who suffers through seasonal allergies, this research is clearly nothing to sneeze at," says Andrew Richardson, an ecologist at Northern Arizona University. The numbers matter. Seasonal allergies already cost billions in healthcare expenses annually, beyond the daily misery they cause for sensitive individuals.
We're a new kind of news feed.
Regular news is designed to drain you. We're a non-profit built to restore you. Every story we publish is scored for impact, progress, and hope.
Start Your News DetoxHow light confuses plants
Two things normally tell plants when to flower and release pollen: temperature and natural light cycles. Artificial light at night — what researchers call ALAN — can't replace sunlight, but it does something more disruptive. "It kind of disturbs their circadian rhythm and confuses plants," explains Lin Meng, the corresponding author from Vanderbilt University. That internal clock disruption stretches the window when plants think it's time to reproduce.
The researchers isolated nighttime lighting's specific effect by modeling data from over a decade, controlling for temperature, precipitation, and other variables. They cross-referenced pollen counts against satellite observations of nighttime brightness and weather records. The pattern emerged clearly: higher artificial light exposure correlated with both higher overall pollen levels in the air and longer pollen seasons.
This matters more than it might seem. Climate change is already extending pollen seasons through warming temperatures. Artificial light is now adding a second mechanism — one that cities can actually influence. A streetlight in Boston or a skyscraper in Philadelphia isn't just a navigation hazard anymore. It's a biological signal that's getting plants out of sync with the seasons.
The research points toward a straightforward tension: urban lighting solves real safety and convenience problems, but those solutions have metabolic costs we're only beginning to measure. As cities grapple with light pollution's effects on birds, insects, and human sleep, allergy seasons offer another reason to reconsider when, where, and how brightly we light the night.
