5 subtle signs you're overheating and at risk of developing heat stroke

• Heat-related illness is more common than ever as global temperatures warm.
• If you feel weak, thirsty, dizzy, or nauseous, you may be at risk of developing heat stroke.

Heat waves are occurring more frequently and at a higher intensity than ever before as the climate warms, and with heat waves comes a risk of heat-related illness.

Heat stroke is the most severe form of overheating, where the body cannot cool itself down and the brain begins to suffer. Neurologic symptoms like confusion, fainting, or even seizures may occur, earning the heat "stroke" diagnosis, emergency physician and climate expert Cecilia Sorenson told Insider.

People who work outside or have underlying medical conditions are at a higher risk of developing heat stroke. Pregnancy and old age are also risk factors, as are certain medications that make people sensitive to sun and heat.

As instances of extreme heat become more common, it is important to know the early signs of overheating that precede heat stroke. If you hydrate and seek shade as soon as you feel unwell, you can avoid more serious illness.

You feel weak or fatigued

Heat fatigue is a mild form of illness or general malaise that happens before full-on heat stroke sets in, Sorenson said. At this point, you may feel tired or weak, but your body temperature is not out of control — yet.

As soon as they start feeling ill, Sorenson urges people to get out of the heat if they can, whether that means seeking out shade or air conditioning.

Weakness and fatigue indicate that you are likely dehydrated and on your way to overheating. Drink cool water or use a wet cloth on your skin, which will accelerate the body's natural cooling process.

You're excessively thirsty

If you feel thirsty after spending time in the heat, your body is likely craving more water.

You lose water by sweating when you are overheated, so it is important to replenish with extra water when it is hot out, especially if you are exercising or working outside.

Persistent dry mouth and changes in urination — lower frequency and dark color — are also signs of dehydration, according to Johns Hopkins Medicine.

You are pale and clammy

While extreme heat is often associated with flushed cheeks and sunburn, early stages of heat exhaustion can actually cause a loss of color.

People who are overheating may appear pale or feel clammy to the touch, as the body tries to cool itself by sweating.

If your skin is dry and flushed red, your core body temperature is likely on the rise and sweating has failed to cool you down. At this point, Sorenson recommends spraying the skin with cold water or using a cool cloth in combination with a fan to cool off.

You have a headache

Headache and dizziness may indicate that your brain is beginning to feel the effects of extreme heat. Both are signs of dehydration, so replenish your water if you haven't already.

Able-bodied, healthy people may not think they are at risk of heat stroke, but anyone can become dehydrated and overheated after spending time in extreme heat.

"You think you know about heat, but you have never seen heat the way we are seeing now," Sorenson, director of the Global Consortium on Climate and Health Education at Columbia University, told Insider. "It is not like the past."

You feel nauseous or crampy

As you become dehydrated in the heat, you may also experience a loss of salt and electrolytes in your sweat. This can lead to some more uncomfortable physical symptoms, like dizziness and nausea.

Electrolytes fuel some of the body's essential functions, and an imbalance can make you feel generally unwell. You also lose electrolytes and fluids if you vomit, so be sure to rehydrate if heat sickness is upsetting your stomach.

An electrolyte imbalance can also cause feelings of cramping in the abdomen, as well as in the arms or legs. Not everyone experiences heat cramps, but it's something to look out for if you are exercising in extreme heat.