A previous study had found that exposure to high levels of particulate matter may reduce the length of survival for patients with breast cancer. Fine particles are microscopic droplets, which can be inhaled and enter your bloodstream through inhalation or ingestion; they’re responsible for giving off pollution in cities where there’s often an overwhelming sense of poor air quality.

However a new Taiwanese study looked at the incidence of breast cancer in areas of Taiwan with varying levels of air pollutants. Air pollutants measured included carbon monoxide (CO), nitric oxide (NO), nitrogen dioxide (NO2), methane (CH4), total hydrocarbon concentration (THC), and fine particulate matter (PM2.5). Researchers in this study tracked the average annual air pollutant concentration from 78 air quality monitoring stations and calculated participants’ long-term average exposure levels to these air pollutants for nearly a decade or until breast cancer diagnosis was made. They found the most urbanised areas of Taiwan had the highest air pollutant concentrations and the highest ratio of new cases of breast cancer.

Sources: Medicine