There’s a misconception that only the firefighters who responded to the World Trade Center attacks on 9/11 risk developing cancer, because of their exposure to asbestos and jet fuel. But in fact, cancer threatens firefighters everywhere, every day.

Although a causal link has not yet been proven, the association between firefighting and a greater cancer risk began to build about 10 years ago. A meta-analysis found that firefighters have a higher risk of multiple myeloma, and possibly a greater risk of contracting non-Hodgkin lymphoma, prostate, and testicular cancers.

Rise in Firefighter Cancer Deaths Since 1950

IAFF / Susan Shaw

From there, more evidence rolled in: Research into Massachusetts firefighters found greater odds of developing brain and colon cancers. Firefighters in their 30s and 40s from five Nordic countries were found last year to have a greater chance of developing prostate and skin cancers. In 2013, researchers studying 30,000 firefighters in three U.S. cities found the profession was associated with “small to moderate increases” in risk for various cancers, particularly respiratory, digestive and urinary malignancies. The study also found that the risk of lung cancer increased with every fire they fought.

“The longer you’re a firefighter, the greater your chance of getting some kind of cancer,” says Susan Shaw, the executive director of the Marine & Environmental Research Institute and a professor of environmental health sciences at the State University of New York in Albany. “These are people who have a gladiator mentality, and they're really tough. [But] now you have a different kind of danger.”

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The problem is our stuff. Possessions make our lives cozy and convenient, but when they catch fire, they become noxious fuel. The cancer rates are being driven up, researchers believe, by chemicals that lace the smoke and soot inside burning buildings. Consumer goods are increasingly manufactured using synthetic materials, and fires are more toxic as a result.

A century ago, we furnished our houses with wood, cloth, metal, and glass. Today, it’s plastics, foams, and coatings—all of which create a toxic soup of carcinogens when they burn. Fire experts say synthetic materials create hundreds of times more smoke than organic ones; flame retardants alone double the amount of smoke and increase toxic gasses 10-fold. Your TV, your kid’s Barbie, your Saran wrap, your couch: all of them can be poisonous when they’re ignited and their fumes are inhaled.

“Every substance, when it burns, changes its chemical structure,” said Timothy Rebbeck, a professor at the Dana-Farber Cancer Institute and the Harvard School of Public Health. “Particularly when you burn something that's synthetic or man-made, you're creating strange compounds that we don't know what they'll do.”

Among the chemicals Shaw and others suspect might be harmful are benzene, found in furniture wax; the formaldehyde in cleaning materials; hydrogen cyanide, which is used in the manufacture of synthetic fibers; stick- and stain-resistant coatings like Scotchgard and Teflon; and the flame-retardants that are added to the foam inside furniture.