It’s officially the beginning of summer and the season is raising temperatures to record levels in many parts of America.

While many may welcome warmer weather, extreme heat is also one of the nation’s top killers — and can exacerbate common conditions with dangerous consequences.

“In the emergency department, when the temperature rises, we see increases in both people experiencing heat-related illness as well as people with worsening of their chronic illnesses,” Dr. Paul Biddinger, chief preparedness and continuity officer at Mass General Brigham, said in a previous statement.

“People at especially increased risk of illness include those with chronic medical conditions, like heart disease, that are made worse by the heat, older adults, young children and some people living in underserved communities,” he said.

From chronic disease to joint pain, heat changes how our body functions, according to experts. Here is a look at some of the common conditions impacted by the heat:

Heart Issues

Heat complicates heart disease, the leading cause of death in the U.S., by requiring the heart to work harder than normal.

When it’s hot, the body sends extra blood to blood vessels, which widen to let heat escape.

“These important changes allow more blood to flow through arteries and veins close to your skin’s surface,” Cleveland Clinic exercise physiologist Michael Crawford explained. “When blood travels there, it’s able to lose a bit of warmth to the air around you.”

But people with clogged arteries might not have that ability.

“You can develop a mismatch between what the heart needs when it’s working harder to face the heat and what the body is able to deliver,” Lauren Siewny, medical director of the Duke University Hospital Emergency Department, told The Washington Post.

Kidney Stones

Kidney disease, which is the country’s eighth-leading cause of death, can also be worsened by high temperatures. That’s because the kidneys need fluids to filter waste and toxins from the blood and to keep blood vessels clear so nutrients can travel to the kidneys, according to the National Kidney Foundation.

When dehydrated, the body can’t do all that as well, possibly leading to permanent kidney damage and raising your risk for kidney stones.

Kidney stones are pebble-like deposits of minerals that form in the kidneys when urine has less water in it, the Mayo Clinic says.

Getting them frequently increases the risk of developing kidney disease because they can block the urinary tract, leading to infections that scar and impair the kidneys.

“Over time, kidney stones that don’t pass can lead to serious complications, which increase the risk for kidney disease,” Dr. Ira Kohn, a urologist at Geisinger Health said in a statement. “Having one kidney stone increases the risk of developing another one.”

Gout

Beyond negatively affecting chronic disease, heat also impacts some of Americans’ most frustrating aches.

More than 91 million U.S. adults are estimated to suffer from arthritis, including 12 million who have gout. Gout is the most common form of inflammatory arthritis, which can be caused by kidney problems and too much of the waste product uric acid in the blood, the Clinic says.

There are multiple forms of inflammatory arthritis, which occur due to inflammation caused by damage in the joints.

Dehydration related to heat can raise levels of uric acid, which causes gout, Dr. N. Lawrence Edwards, a rheumatologist and chairman of the Gout Education Society, says.

Both heat and humidity can also increase inflammation and American Heart Association research from 2024 shows it may impair immune cells, leading to inflammation.

“With rising global temperatures, the association between heat exposure and a temporarily weakened response from the immune system is a concern because temperature and humidity are known to be important environmental drivers of infectious, airborne disease transmission,” Daniel W. Riggs, an assistant professor of medicine at the University of Louisville, noted.

“Thus, during the hottest days of summer people may be at higher risk of heat exposure, they may also be more vulnerable to disease or inflammation,” he said.

Headaches

Lastly, you may be wondering why your migraines get worse during heat waves.

That’s because changes in pressure and temperature can lead to head pain. So can dehydration, according to the American Migraine Foundation.

“About 1/3 of people with migraine say dehydration is a trigger, and for some, even the slightest hint of dehydration can be the fast track to debilitating head pain,” it said.