(NEXSTAR) – In an average year, heat takes more lives in the U.S. than hurricanes, tornadoes and earthquakes combined. The Centers for Disease Control and Prevention estimates the death toll of extreme heat waves to be around 1,220 annually.

But the way heat kills people is less obvious than other violent natural disasters. The difference between life and death can be decided by just a few degrees, experts say.

Your body’s resting temperature is supposed to be around 98.6 degrees Fahrenheit. If it gets seven degrees higher than that, the results can be catastrophic.

“We routinely will see core temperatures greater than 104, 105 degrees during some of the heat episodes,” Dr. Neil Gandhi, emergency medicine director at Houston Methodist Hospital, told the Associated Press. Another degree or three and such a patient is at high risk of death, he said.

3 ways heat kills

High body temperature is dangerous because it can start to cause organ failure.

When inner body temperature gets too hot, the body redirects blood flow toward the skin to cool down, said Ollie Jay, a professor of heat and health at the University of Sydney in Australia. But that diverts blood and oxygen away from the stomach and intestines, and can allow toxins normally confined to the gut area to leak into circulation.

“That sets off a cascade of effects,” Jay said. “Clotting around the body and multiple organ failure and, ultimately, death.”

But the bigger killer in heat is the strain on the heart, especially for people who have cardiovascular disease, Jay said.

It again starts with blood rushing to the skin to help shed core heat. That causes blood pressure to drop. The heart responds by trying to pump more blood to keep you from passing out.

“You’re asking the heart to do a lot more work than it usually has to do,” Jay said. For someone with a heart condition “it’s like running for a bus with a dodgy (hamstring). Something’s going to give.”

The third main way is dangerous dehydration. As people sweat, they lose liquids to a point that can severely stress kidneys, Jay said.

Dehydration can progress into shock, causing organs to shut down from lack of blood, oxygen and nutrients, leading to seizures and death, said Dr. Renee Salas, a Harvard University professor of public health and an emergency room physician at Massachusetts General Hospital.

Heat stroke warning signs

The best way to protect yourself from heat-related death is to cool your body down by any means possible. Emergency rooms often turn to cold water immersion as a quick way to drop the body’s temperature.

Signs your health may be impacted by dangerous heat include:

  • Dizziness
  • Thirst
  • Profuse sweating
  • Nausea
  • General weakness

If you feel any of the above signs of heat exhaustion, you should move to a cooler area and drink water.

If action isn’t taken, heat exhaustion can turn into heat stroke. Signs of heat stroke include confusion, dizziness and losing consciousness. Those are signs you should call 911 and seek urgent medical attention.

The Associated Press contributed to this report.