As temperatures and humidity soar outside, what’s happening inside the human body can become a life-or-death battle decided by just a few degrees.

The critical danger point outdoors for illness and death from relentless heat is several degrees lower than experts once thought, say researchers who put people in hot boxes to see what happens to them.

With much of the United States, Mexico, India and the Middle East suffering through blistering heat waves, worsened by climate change, several doctors, physiologists and other experts explained to The Associated Press what happens to the human body in such heat.

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Heat waves can raise your body temperature

The body’s resting core temperature is typically about 98.6 degrees Fahrenheit.

That’s only 7 degrees away from catastrophe in the form of heatstroke, said Ollie Jay, a professor of heat and health at the University of Sydney in Australia, where he runs the thermoergonomics laboratory.

Dr. Neil Gandhi, emergency medicine director at Houston Methodist Hospital, said during heat waves anyone who comes in with a fever of 102 or higher and no clear source of infection will be looked at for heat exhaustion or the more severe heatstroke.

“We routinely will see core temperatures greater than 104, 105 degrees during some of the heat episodes,” Gandhi said. Another degree or three and such a patient is at high risk of death, he said.

How heat kills

Heat kills in three main ways, Jay said. The usual first suspect is heatstroke — critical increases in body temperature that cause organs to fail.

When inner body temperature gets too hot, the body redirects blood flow toward the skin to cool down, Jay said. 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 dodgy (hamstring). Something’s going to give.”

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

Many people may not realize their danger, Houston’s Gandhi 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.

“Dehydration can be very dangerous and even deadly for everyone if it gets bad enough — but it is especially dangerous for those with medical conditions and on certain medications,” Salas said.

Dehydration also reduces blood flow and magnifies cardiac problems, Jay said.

Intense heat can ‘fry’ your brain

Heat also affects the brain. It can cause a person to have confusion, or trouble thinking, several doctors said.

“One of the first symptoms you’re getting into trouble with the heat is if you get confused,” said University of Washington public health and climate professor Kris Ebi. That’s little help as a symptom because the person suffering from the heat is unlikely to recognize it, she said. And it becomes a bigger problem as people age.

One of the classic definitions of heat stroke is a core body temperature of 104 degrees “coupled with cognitive dysfunction,” said Pennsylvania State University physiology professor W. Larry Kenney.

Heat and humidity are a dangerous duo

Some scientists use a complicated outside temperature measurement called wet bulb globe temperature, which takes into account humidity, solar radiation and wind. In the past, it was thought that a wet-bulb reading of 95 Fahrenheit was the point when the body started having trouble, said Kenney, who also runs a hot box lab and has done nearly 600 tests with volunteers.

His tests show the wet-bulb danger point is closer to 87. That’s a figure that has started to appear in the Middle East, he said.

And that’s just for young healthy people. For older people, the danger point is a wet bulb temperature of 82, he said.

“Humid heat waves kill a lot more people than dry heat waves,” Kenney said.

When Kenney tested young and old people in dry heat, young volunteers could function until 125.6 degrees, while the elderly had to stop at 109.4. With high or moderate humidity, the people could not function at nearly as high a temperature, he said.

“Humidity impacts the ability of sweat to evaporate,” Jay said.

How to cool down heat exhaustion patients

Heatstroke is an emergency, and medical workers try to cool a victim down within 30 minutes, Salas said.

The best way: Cold water immersion. Basically, “you drop them in a water bucket,” Salas said.

But those aren’t always around. So emergency rooms pump patients with cool fluids intravenously, spray them with misters, put ice packs in armpits and groins and place them on a chilling mat with cold water running inside it.

Sometimes it doesn’t work.

“We call it the silent killer because it’s not this kind of visually dramatic event,” Jay said. “It’s insidious. It’s hidden.”

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On social media, castor oil has become a popular trend for various uses, from hair growth to weight loss.

There have been millions of posts about the vegetable oil on TikTok, with many creators sharing how they’ve used it to improve their health.

In more controversial cases, creators have applied castor oil directly to their belly buttons — and have even taken to drinking it as a detox and weight-loss method, since the FDA has approved castor oil as a natural laxative.

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While some people on the internet have reported positive results, experts are warning that castor oil consumption could be dangerous for overall health.

Registered dietitian Ilana Muhlstein told Fox News Digital she has “never heard of castor oil being used for anything other than its traditional applications.” 

The Los Angeles-based expert assumed that a primary use is for short-term, mild weight loss, since castor oil acts as a laxative.

“Laxatives can dehydrate you and cause dependency,” she said. “There are much safer alternatives.” 

She added, “If you’re having trouble in the bathroom, try increasing your water intake, adding more fiber to your diet and getting more exercise. Speak with your doctor or dietitian if you have any questions.”

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Katrina Mattingly, M.D., chief medical officer at Option Medical Weight Loss in Chicago, said castor oil is a “tried-and-true, old-school laxative.”

She told Fox News Digital in an email, “The first thing that comes to mind is diarrhea.”

Castor oil is a “tried-and-true old school laxative” with a “distinct taste,” one doctor told Fox News Digital. But doctors warn about its use for weight loss.  (iStock)

“I remember my 97-year-old grandmother giving it to us as kids, along with prune juice, when our GI systems needed help moving things along,” Mattingly said.

Castor oil “hastens our bodies’ elimination of solid waste products and also rids the body of essential water,” the expert noted.

While this can trigger weight loss, Mattingly said that “along with all the solid waste and essential water going down the toilet are essential vitamins and minerals, such as potassium and chloride” — which can lead to deficiencies.

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While castor oil can be helpful in relieving occasional constipation, overusing it as a laxative can lead to the bowels becoming dependent on laxatives, Mattingly warned, “making it difficult to go naturally on your own.”

The obesity doctor emphasized that she would not recommend castor oil for weight loss in any capacity.

One doctor only recommends drinking castor oil in small amounts for occasional constipation.  (iStock)

“Although castor oil has been in use for centuries for a variety of reasons, from body detoxification to vision problems to labor induction, there’s no safety data to recommend routine use for any of these conditions, except constipation,” she said.

Current scientific studies and research do not support its use solely for the purpose of weight loss, the doctor noted.

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Mattingly said she would recommend ingesting castor oil in “small amounts” only for occasional bouts of constipation if it has worked in the past.

“Just remember to hydrate to replace the fluid loss, and if you have long-term or chronic constipation, that warrants a trip to your physician.”

‘Massive detox’ or health hazard?

Women’s health expert Dr. Mindy Pelz advocated for the use of castor oil packs to regulate organ function and move toxins through the body.

The California-based doctor claimed that castor oil can absorb through the skin and move into the organs “very easily.”

Castor oil application can spark a “massive detox,” one doctor said. (iStock)

“When it goes into our system, it creates dilation,” Pelz said to Fox News Digital. “It’s so simple, and so inexpensive … You could just rub it over your liver and gallbladder. You need castor oil to stay on there for two hours for it to … start to dilate these organs.”

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Pelz recommended applying castor oil at night, up to three times a week, for a “massive detox that opens the whole system up.”

The FDA has approved castor oil as a natural laxative. (iStock)

Mattingly, however, countered that castor oil “does not show promise in having inflammatory, antimicrobial properties or antioxidant properties.”

And while viral social media claims are often based on personal experiences, Mattingly noted that certain applications may not have the same effect on everyone.

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“When it comes to medical weight loss, leave that to the experts to ensure you are undergoing a safe and effective plan that won’t leave you miserable or taking that dreaded trip to the ER,” she advised.

Other castor oil applications

There are a few traditional applications for castor oil, including applying it to the scalp or eyelashes to promote hair growth, as well as using it on the belly button for better sleep, Muhlstein said.

“Some people say it helps ease muscle tension and promotes deeper sleep,” she said. “Just be cautious,” she added, “because I’ve heard that using too much of it can make you feel lethargic.”

“Perhaps future studies will give us another resounding medicinal use for [castor oil] other than constipation,” one doctor said. (iStock)

Another potential use for castor oil is as a topical treatment for skin irritations or scars, Muhlstein added.

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“People have reported positive results,” she said. “So, if you’ve got any annoying skin issues, it might be worth giving it a try, but always consult with a dermatologist for bigger issues.”

Mattingly recommended rubbing castor oil on your stomach or skin as a moisturizer only — but not for weight loss.

“Also, castor oil can have an unforgettable smell,” she warned. “So be prepared for this, particularly if using it on the face or hair.”