Polluted air raises the chances of irregular menstrual cycles among teenage girls, a new Boston University School of Medicine study reports. Studying the records of 34,832 women and linking that information with levels of pollutants when the women were 14 to 18 years old, researchers concluded that teenage girls in polluted areas have a slightly greater likelihood of menstrual irregularity and take longer to achieve regularity in high school and early adulthood. It may also put them at long-term risk of other hormone-related problems, researchers warned.