Artificial Night Lighting Linked to Seasonal Allergies
Gardens Illustrated
Artificial light at night, long known for its effects on wildlife and human circadian rhythms, may also pose a growing public health risk by extending pollen seasons and increasing allergen exposure in cities, according to new research conducted in the northeastern United States. The study finds that plants exposed to artificial light at night (ALAN) produce pollen over a longer period, creating what researchers describe as a significant public health issue. “Seasonal allergies cost billions of dollars in healthcare and disrupt the lives of people who are sensitive,” said Andrew Richardson, Ecology Researcher, Northern Arizona University.
Flowering and pollen production in plants are primarily influenced by temperature and light. While artificial light does not replace sunlight, it alters plants' circadian rhythms and confuses them, explained Lin Meng of Vanderbilt University, in an interview with Mongabay.
To isolate the effects of nighttime lighting, researchers controlled for temperature and precipitation using statistical models. They analyzed atmospheric pollen counts alongside satellite observations of nighttime light exposure and climate data. The study examined a 12-year period, from 2012 to 2023, focusing on the northeastern United States, including major metropolitan areas such as New York, Boston, and Philadelphia.
The findings show that higher exposure to artificial light at night is associated with increased airborne pollen levels and a longer pollen season, extending it by roughly one to two weeks. Climate change, particularly rising temperatures, is already known to lengthen pollen seasons, but Meng said the study suggests that the impact of artificial nighttime lighting is comparable in magnitude. “Together, warmer temperatures and nighttime lighting act as cumulative factors, producing effects greater than either one alone,” Meng said.
Brian Enquist, Ecologist, University of Arizona, noted that urban plants are often ornamental species with greater access to water and less competition for resources, factors that may further influence pollen production. “Future work will need to disentangle the effects of light on urban species composition, water availability and tree structure,” Enquist said, adding that urban ecosystems influence biological rhythms in many ways and that artificial light could be part of that broad suite of factors.
Seasonal allergies and asthma represent a major public health burden in the United States, affecting tens of millions of people each year. An estimated 10% to 25% of the population experiences symptoms of allergic rhinitis or asthma, and allergy-related conditions affect nearly one-third of adults. Exposure is driven largely by pollen from wind-pollinated trees and grasses that release large quantities of easily dispersed particles.
Climate change has been identified as a key driver behind earlier, longer and more intense pollen seasons. In urban environments, these effects are amplified by factors such as the heat island effect, air pollution and increasing exposure to artificial light at night. Among these, ALAN has been one of the least studied despite its rapid global expansion and its ability to disrupt natural light-dark cycles that regulate plant phenology.
The findings also carry implications for urban planning and tree management. Many commonly planted urban tree species are highly sensitive to photoperiod and produce large amounts of pollen, making them particularly responsive to artificial lighting. Incorporating allergenicity and light sensitivity into species selection, along with strategies to reduce light pollution, such as lowering illumination levels, shielding fixtures or limiting blue light, could help reduce allergen exposure.
The authors note that further research is needed to clarify causal mechanisms and examine interactions between artificial lighting and other environmental stressors, such as air pollution. Still, the consistency of results across multiple locations and over more than a decade suggests that managing artificial night lighting should be viewed not only through the lens of energy efficiency or ecological conservation, but also as a matter of public health and urban resilience.