Nearly one in four U.S. adults have seasonal allergies. So do one in five kids. Most of those allergies are to mold spores or pollen from ragweed, grasses and trees. Now, a study finds, flashy billboards, streetlights and bright buildings are extending pollen season in cities.
Indeed, that season can now run two months longer there than in rural areas.
Explainer: What are allergies?
Why? Plants are sensitive to changes in day length — how many hours of sunlight they get. They also take cues from changes in temperature and rainfall. In spring, days gradually lengthen at the same time that soil and air temps rise. These cue tree buds to swell and break open. Likewise, longer and warmer summer days prompt plants to flower and release pollen.
Exposure to lights at night can “disrupt the natural day-length signal,” says Lin Meng. She’s an ecologist at Vanderbilt University in Nashville, Tenn. She’s also an author of the new study. Night lighting makes plants think days are longer than they really are.
Past studies ...
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