The International Agency for Research on Cancer has upgraded how it classifies the risks associated with firefighting.
The group recently released a report based on studies led by the University of Arizona Health Sciences and the Tucson Fire Department that lists the occupation as carcinogenic.
The agency is part of the World Health Organization and had previously classified firefighting as possibly carcinogenic.
Researchers found evidence that occupational exposure to carcinogens as a firefighter causes mesothelioma and bladder cancer.
Limited evidence also shows dangers of colon, prostate and testicular cancers along with melanoma and non-Hodgkin lymphoma.
Researchers say 15 million firefighters worldwide are exposed to various combustion products including flame retardants in textiles and other pollutants along with other job hazards.
Leaders of the study are calling for ways to reduce exposures to carcinogens in firefighting.