The World Health Organization has now classified outdoor air pollution as a human carcinogen. According to a press release from the International Agency for Research on Cancer ("IARC"), based on its review of available scientific literature, there is now sufficient evidence that exposure to outdoor air pollution causes lung cancer. As a result, IARC has classified outdoor air pollution as "carcinogenic to humans". In addition, IARC noted that there was also a positive association between outdoor air pollution and an increased risk of bladder cancer. According to IARC's Director, "[c]lassifying outdoor air pollution as carcinogenic to humans is an important step. There are effective ways to reduce air pollution and, given the scale of the exposure affecting people worldwide, this report should send a strong signal to the international community to take action without further delay." Unfortunately, IARC's press release provides little guidance on how to avoid exposure to what now is a pervasive carcinogenic substance; we will have to stay tuned for more information from the World Health Organization on this important issue.