A study published in the January 2026 issue of the scientific journal PNAS Nexus reveals that nocturnal artificial lighting contributes to lengthening the atmospheric pollen season in the Northeastern United States. As temperatures are already rising due to climate change, urban lighting now appears as an additional environmental factor capable of intensifying pollen exposure and thus allergic symptoms.
It’s proven: artificial light indeed alters flowering times and pollen release
Nocturnal artificial lighting, stemming from streetlights and LED signs, disrupts the natural cycles of light and dark. According to an American study published in the journal PNAS Nexus, this light directly influences the phenological events of plants, notably flowering and pollen release. Indeed, the researchers show that greater exposure to lighting is associated with an earlier start to the season, but also a later end, even after accounting for temperatures and precipitation.
The researchers analyzed 12 years of data, from 2012 to 2023, across numerous monitoring stations in the Northeastern United States. They compared areas with strong nocturnal lighting exposure to less illuminated zones. The results indicate that 27% of pollen-season days are classified as severe in high-light areas, versus 17% in less exposed areas. Thus, lighting contributes not only to lengthening the season, but also to increasing the intensity of pollen episodes.
Nocturnal artificial light: a standalone factor
Lighting does not replace the role of temperatures, but it acts in concert with them, the researchers explain. Nocturnal artificial lighting is indeed an independent factor, even when researchers adjust their models for thermal variation. In other words, while higher temperatures already push the pollen season earlier, lighting amplifies this effect further in urban environments.
Moreover, the lighting comes from multiple sources: public streetlights, buildings, illuminated signs, motor traffic. These sources have proliferated with the widespread adoption of LEDs, known for their high intensity and low energy cost. However, while these devices reduce electrical consumption, they emit light rich in wavelengths likely to affect plant physiology. The most urbanized areas of the Northeast United States combine high light density with a high pollen concentration, which reinforces the risk for allergic populations.
Urban lighting: ways to mitigate the impact on flora exist
As a result, nighttime lighting raises public health concerns. The researchers estimate that the rise in the number of severe pollen days increases urban residents’ cumulative exposure. Thus, with 27% of severe days in brightly lit areas versus 17% elsewhere, the gap represents a meaningful relative increase in allergy risk. For people with rhinitis or allergic asthma, this could mean several extra weeks of symptoms.
Furthermore, the study opens a debate about city light management. While lighting ensures safety and economic activity, it also becomes a standalone environmental factor. Consequently, some experts point to mitigation strategies such as reducing light intensity, redirecting beams toward the ground, or choosing LEDs with spectrums less disruptive to vegetation. The question, therefore, is no longer solely about temperatures and climate, but also about the very organization of urban lighting, whose impact on the pollen season could become a central issue for local environmental policy.
