Women living in urban areas may be more likely to need breast cancer treatment, researchers have said.
A study involving 972 women, carried out by the Princess Grace Hospital, a private hospital in London, found that women in the city have much denser breast tissue.
Dense breasts are made up of more glandular tissue and have previously been found to make a woman four times more likely to develop breast cancer.
The findings may be due to air pollution which contains tiny particles that mimic female hormones.
Researcher Professor Kefah Mokbel commented: "Women who live or work in cities should pay greater attention to breast screening. Ironically, uptake of breast screening is lower in cities like London than in the countryside."
Professor Mokbel also called for better traffic management to reduce emissions.
"This is an important issue for the public and politicians, and it's vital that we raise awareness of the link we have found," he added.