Heat stress can affect anyone — whether you are exercising outdoors, commuting in the city or spending time in a warm home. The good news: Most heat‑related illnesses are preventable.

Keeping It Cool

Sweating is your body’s main cooling tool. It helps release heat and regulate your internal temperature. But sweat only cools your body if it evaporates. High humidity, certain health conditions, medications, and lack of water or shade can make evaporation harder.

When that happens, your risk of overheating increases.

What Is a Heat‑Related Illness

The types of heat-related illnesses range from mild to life‑threatening. The five most common are sunburn, heat rash, heat cramps, heat exhaustion and heat stroke.

1. Sunburn

Sunburn is one of the most common heat‑related problems. It happens when ultraviolet (UV) rays damage the skin, sometimes in as little as 15 minutes. Repeated sunburns increase the long‑term risk of skin cancer.

Daily sun protection makes a difference. Use a broad‑spectrum sunscreen and reapply at least every two hours while outdoors. The American Academy of Dermatology recommends SPF 30 or higher. Hats, sunglasses, lightweight clothing and shade provide added protection.

Severe sunburn can cause blisters, fever, chills or nausea. You should consider talking with your primary care physician or a dermatologist if you have any of the following symptoms:

• Blisters that cover a large area of skin, such as more than 20% of your body. Your physician can assess your burns to decide if you need more treatment. Treatment could include medication for inflammation or medicated cream to help your skin recover.
  
• A high fever, chills or nausea. These could be signs of severe sunburn (also known as sun poisoning). If you have this, you might need IV (into the vein) fluids to treat severe dehydration. You may also need steroids or other medication to help manage pain.
  
• Signs of infection, such as swelling or pus, or blisters that turn yellow or red over time. Peeling sunburned skin can expose the new skin underneath to germs. This could cause an infection that may require antibiotics.

2. Heat rash

Heat rash happens when sweat gets trapped in the skin, creating small red bumps. It often shows up on the neck, chest, underarms or groin, especially in hot, humid weather.

Loose, breathable clothing and access to shade and air‑conditioning can help prevent flare-ups. Keep irritated skin clean and dry. Light lotions or powders may also help ease symptoms.

3. Heat cramps

Heat cramps are painful muscle spasms that typically affect the legs, arms or abdomen (stomach). They often occur after physical activity in hot weather and may be an early sign of a more serious heat‑related illness.

Heavy sweating leads to the loss of water and salt. When your sodium levels drop too low, muscle cramps can develop. Dehydration increases the risk.

If heat cramps occur, stop activity and move to a cool place. Drink water or an electrolyte beverage to help replace lost fluids and minerals. Gentle stretching or light massage may also help.

4. Heat exhaustion

Heat exhaustion develops when your body overheats and has difficulty cooling itself down. It may build over several days or come on quickly during extreme heat, especially when you are active. If left untreated, it can lead to heat stroke.

Common symptoms include:

• Body temperature above normal, but below 104 degrees Fahrenheit
• Weakness or fatigue
• Cool, pale or clammy skin
• Fast, weak pulse
• Increased thirst
• Dizziness or headaches
• Nausea or vomiting
• Fainting (passing out)

If you have signs of heat exhaustion, move to a cooler place, remove excess clothing, and hydrate with water or an electrolyte drink. If symptoms last longer than one hour, worsen, or do not improve with cooling and hydration, seek medical care.

5. Heat stroke (medical emergency)

Heat stroke is the most severe heat‑related illness and requires emergency care. It occurs when the body can no longer cool itself and body temperature rises rapidly, putting organs at risk. It can progress within minutes.

Signs of heat stroke include:

• High body temperature, typically above 104 degrees Fahrenheit
• Hot, red or dry skin
• Rapid heart rate
• Confusion or disorientation
• Loss of consciousness
• Nausea or vomiting
• Rapid or shallow breathing
• Throbbing headache
• Hallucinations or dizziness

“In the emergency department, we see how fast heat stroke can progress,” says Jeffrey H. Bohmer, MD, an emergency medicine physician and associate chief medical officer at Northwestern Medicine. “Early recognition and rapid cooling can be lifesaving.”

In severe cases, heat stroke can damage the brain and other vital organs, which can be fatal. If you suspect that you or someone else is experiencing heat stroke, call 911 or your local emergency number immediately.

Staying Safe in Extreme Heat

Extreme heat is becoming more common, with heat alerts increasing across the United States. Heat forecast tools can help you stay aware of dangerous conditions. You can find local heat advisories and safety tips at heat.gov.

Your heat tolerance depends on many factors: age, medical conditions, alcohol use, medications and circulation issues.

More ways to stay safe in hot weather:

• Plan outdoor activities in the early morning or evening.
• Spend time in air‑conditioned spaces.
• Wear light‑colored, loose‑fitting clothing.
• Take cool showers.
• Avoid crowded places.
• Pace yourself and rest often.
• Pay attention to heat advisories and heat risk levels.
• Be aware of increased risk for people with certain medical conditions, such as diabetes.
• Check in on neighbors, older adults and people who may be at higher risk.

Heat‑related illness is serious, but it’s often preventable. Paying attention to hydration, your environment and early symptoms of heat-related illness can go a long way in keeping you and your family safe.

“If you start to feel unwell in the heat, don’t push through it,” says Dr. Bohmer. “Stop, cool down and hydrate — your body is sending you an important warning.”