It’s not the flames or even the smoke. It’s the toxins that escape during a fire that are causing high cancer rates among the nation’s firefighters.

In the new film “Only the Brave,” 19 members of the elite Granite Mountain Hotshots, a skilled team of firefighters from Arizona, die when a bolt of lightning ignites a fire and entraps the men.

The real-life deaths of these men, who’ve been called the Navy SEALs of firefighting, is how many people still think most firefighters die.

But a surplus of new evidence shows that it’s not just the flames themselves or the inhalation of smoke that’s taking our firefighters in historically large numbers.

It’s the toxic and often carcinogenic soot that’s left behind on the fire gear and the firefighters themselves.

In fact, neither heart disease nor lung disease is the number one killer of firefighters in 2017.

It’s cancer.

And it’s largely because fires have gotten far more toxic in the past 25 years.

Just ask Steve Fisher.

A firefighter and family man from Portland, Oregon, Fisher didn’t know too much about the link between firefighting and cancer when he started his career.

That all changed in 1998, when a captain with the Eugene Fire Department sent Fisher and his fellow firefighters a clear message.

“When we got back to the firehouse, my captain would always say to everyone, ‘Hit the shower and wash that cancer off your body.’ He was the first one in my career that I ever heard talk about that in the fire service,” Fisher told Healthline.

It still wasn’t enough — 11 years later, Fisher was diagnosed with testicular cancer.

An Oregon law that recognizes the growing body of evidence linking firefighting and cancer was approved by the state Legislature just in time to help Fisher.

He had surgery and underwent chemotherapy. He’s now in remission.

The list of cancers in Oregon that are presumed to be connected to firefighting include testicular, lymphoma, leukemia, myeloma, lung, brain, breast, and colorectal.

“I was the first claim under the new presumptive law, which says that an insurance company has to prove that my cancer came from somewhere other than firefighting,” said Fisher, who’s now an active member of the Firefighter Cancer Support Network (FCSN), a national nonprofit leader in the battle against occupational cancer for more than a decade.

Since 2005, FCSN has provided assistance and one-on-one mentoring to thousands of cancer-stricken firefighters and their families nationwide.

Fisher said that until laws like the one in Oregon are passed, insurance companies’ first move will typically be to deny the firefighter’s claim and leave it up to the employee to fight it.

“Since my claim, I would say most firefighters in Oregon have thankfully not had to go through [the] same fight as I did,” Fisher said.

Joseph Finn, the fire commissioner and head of the Boston Fire Department, said the increasing cancer danger is because of the plastics that are so commonly found now in most structures, as well as the fire retardants used on furniture and other things found in homes and offices.

“Almost everything in modern buildings today is made of processed plastic. And it burns very hot and fast and gives off more carcinogenic by-product than traditional fires did in years gone by,” Finn told Healthline.

This has led to a national and global cancer crisis among firefighters, he said.

“Most people don’t know that cancer has been the number one cause of deaths among firefighters in the United States for the past 12 years,” Finn said.

“Every fire, whether it’s a car fire, or a room, or a pot on the stove — all of those give off carcinogens. We urge firefighters to be aware of this,” he added.

He noted that these toxins don’t just enter the body via inhalation.

“It can come right through the skin,” he said.

A recent study by researchers at the University of Ottawa (Université d’Ottawa) confirmed that firefighters absorb harmful chemicals, including polycyclic aromatic hydrocarbons (PAHs), through their skin.

With the help of a “very supportive union and mayor,” Finn is bringing about positive changes in the way fire departments are run.

He hopes the efforts will continue to save firefighters’ lives not only in Boston, but nationwide.

“It goes beyond awareness,” Finn said.

The key for firefighters is to have the proper training and equipment, including fire gear that protects the entire body.

It’s also crucial to thoroughly clean all equipment and the body after every fire.

And it doesn’t help that fire stations use diesel fuel, and that firefighters deal with great stress and often go far too many hours without sleep.

All these things contribute to a culture that’s conducive to cancer, multiple sources told Healthline.

“Before they even drink water after a fire, cleaning up can prevent cancer,” said Finn.

His department provided cancer prevention training to 1,450 firefighters in 2015 and this training will continue with all new recruits.

Multiple peer-reviewed studies have shown that firefighters have higher cancer risk than the general population, and their risks are significantly higher for some specific types of cancer.

Multiple experts interviewed by Healthline support a national firefighter cancer registry to increase awareness of the relationship between exposure and cancer development.

According to the FCSN, cancer is the most dangerous threat to a firefighter’s health and safety.

FCSN’s inaugural two-day Health and Wellness Symposium at the Pasadena Convention Center, held on Nov. 30 to Dec. 1, focused on cancer prevention best practices, behavioral wellness, personal protective equipment research, and navigating through the workers’ compensation system.

Bryan Frieders, deputy chief of the Pasadena Fire Department and president of the FCSN, emphasized that there are a lot of false fire cancer statistics available on the internet.

But here are some real numbers:

* According to data from the International Association of Fire Fighters (IAFF), cancer caused 61 percent of deaths for career firefighters in the line of duty from Jan. 1, 2002 to Dec. 31, 2016.

* Cancer caused 70 percent of line-of-duty deaths for career firefighters in 2016, according to IAFF.

* Firefighters have a 9 percent higher risk of being diagnosed with cancer than the general U.S. population, according to the National Institute for Occupational Safety and Health (NIOSH), a part of the Centers for Disease Control and Prevention (CDC).

* Firefighters have a 14 percent higher risk of dying from cancer than the general U.S. population, according to NIOSH.

FCSN supports the Firefighter Cancer Registry Act, a bill that was introduced in Congress in February with 76 original sponsors.

It passed the House in September and is expected to go to the Senate soon for consideration.

In a 2013 paper, “Taking Action Against Cancer in the Fire Service,” FCSN provided details about recognizing and reducing firefighters’ cancer risks.

The paper included 11 immediate actions firefighters should take to protect themselves, their families, and their fellow firefighters.

FCSN has also helped national and local media outlets get information about cancer and firefighting to the public.

In September 2015, FCSN helped a reporter from The Atlantic research cancer in the fire service, and states’ varying presumptive laws for workers’ compensation and other benefits.

Also in 2015, an NBC affiliate in Denver presented a three-part series on cancer in the fire service.

However, if President Donald Trump has his way, a review of flame retardants and other toxins in homes, offices, and industrial plants across the United States may be minimized, according to reports.

Instead of following President Barack Obama’s proposal to review the use of chemicals that result in toxic exposures, the Trump administration reportedly wants to limit the review to products still being manufactured and entering the marketplace.

Firefighter groups, health workers, consumer advocates, members of Congress, and environmental groups all say we can’t ignore the 8.9 million tons of asbestos-containing products.

Asbestos is known to cause mesothelioma, a type of cancer.

Patrick Morrison, assistant general president for health and safety at the International Association of Fire Fighters, told The Associated Press last month:

“Hundreds of thousands of firefighters are going to be affected by this. It is by far the biggest hazard we have out there. My God, these are not just firefighters at risk. There are people that live in these structures and don’t know the danger of asbestos.”

NIOSH conducted a mortality study involving 30,000 firefighters that was published in 2013.

The NIOSH study is particularly significant because it spans the entire country — from San Francisco to Chicago to Philadelphia — and decades (1950 to 2009).

Phase 1 of the study found statistically significant excess cancer mortality and incidence rates for firefighters compared with the general population.

The NIOSH study noted cancers of the esophagus, intestine, lung, kidney, and oral cavity, as well as mesothelioma.

NIOSH concluded that firefighters contract mesothelioma at “twice the rate” of other U.S. residents.

Meanwhile, 37 states now reportedly recognize the link between cancer and firefighting for workers’ compensation, medical benefits, or death benefits.

The coverage and benefits provided vary widely state by state.

Ohio, Georgia, and New York are reportedly the latest states to pass a firefighter cancer presumption law as of this month.

Efforts to pass firefighter cancer-related legislation are also under way in Florida and several other states.