A large study reveals that artificial nighttime light plays a key role in extending the pollen season in urban areas.
Does city light really disrupt the pollen cycle?
Under our street lights, a discreet disruptor attacks our immune system. According to this study published on January 20, 2026 by PNAS Nexus, artificial nighttime light – or ALAN (Artificial Light At Night) – is associated with a longer and more severe pollen season in large metropolises in the northeast of the United States. Led by Lin Meng and his colleagues, the research is based on the analysis of 12 years of pollen data, cross-referenced with satellite data on light pollution and climate records.
Scientists have observed that areas heavily exposed to artificial light experience an earlier start to the season, a later end, and a significantly longer overall duration. Artificial nighttime light advances the start and delays the end of pollen activity, thereby extending the length of the pollen season. In the brightest cities, plants seem to push back the natural seasonal limits.
Up to 300 pollen days per year in some cities
The data shows an advance in the start of the season of around 20 days in areas with high light exposure. But it is especially the end of the season that surprises: instead of stopping around day 270 of the year, it regularly exceeds day 300. As a result, certain urban areas like New York or Philadelphia experience nearly 10 months of pollen.
The average length of the season in lit areas exceeds 240 days, compared to 170 to 210 days in less affected regions. This prolonged exposure has a direct impact on the health of city dwellers. In environments exposed to artificial nighttime light, 27% of pollen season days were classified as having severe exposure, compared to only 17% in areas with little or no exposure.
Light pollution, an underestimated risk for allergy sufferers
This publication highlights a blind spot in public health policies. Until now, global warming was identified as the main factor in the lengthening of the pollen season. Now, artificial nighttime light appears as another lever, still little discussed, but directly linked to the urban environment.
Artificial light at night represents an underestimated allergy risk factor, which should be integrated into environmental public health and urban planning strategies.
The avenues mentioned in the study: better regulate public lighting, limit certain light emissions, and take these parameters into account in urban development strategies, particularly in cities where light pollution and the prevalence of allergies are high.