Your body has a natural cooling system. It is always working to maintain a safe body temperature. Sweating helps your body cool down.

When you exercise in the heat, your cooling system has to work harder. Your body sends more blood to your skin and away from your muscles. This increases your heart rate. You sweat a lot, losing fluids in your body. If it is humid, sweat stays on your skin, which makes it hard for your body to cool itself.

Warm-weather exercise puts you at risk for heat emergencies, such as:

• Heat cramps. Muscle cramps, usually in the legs or stomach (caused by loss of salt from sweating). This may be the first sign of overheating.
• Heat exhaustion. Heavy sweating, cold and clammy skin, nausea and vomiting.
• Heatstroke. When the body temperature rises above 104°F (40°C). Heatstroke is a life-threatening condition.

Children, older adults, and obese people have a higher risk for these illnesses. People taking certain medicines and people with heart disease also have a higher risk. However, even a top athlete in superb condition can get heat illness.

Try these tips to help prevent heat-related illness:

• Drink plenty of fluids. Drink before, during, and after your workout. Drink even if you do not feel thirsty. You can tell you are getting enough if your urine is light or very pale yellow.
• Do not drink alcohol, caffeine, or drinks with a lot of sugar, such as soda. They can cause you to lose fluids.
• Water is your best choice for less-intense workouts. If you will be exercising for a couple of hours, you may want to choose a sports drink. These replace salts and minerals as well as fluids. Choose lower-calorie options. They have less sugar.
• Make sure the water or sports drinks are cool, but not too cold. Very cold drinks may cause stomach cramps.
• Limit your training on very hot days. Try training in the early morning or later at night.
• Choose the right clothing for your activity. Lighter colors and wicking fabrics are good choices.
• Protect yourself from direct sun with sunglasses and a hat. Do not forget sunscreen (SPF 30 or higher).
• Rest often in shady areas or try to stay on the shady side of a walking or hiking trail.
• Do not take salt tablets. They can increase your risk for dehydration.

Know the early warning signs of heat exhaustion:

• Heavy sweating
• Tiredness
• Thirsty
• Muscle cramps

Later signs may include:

• Weakness
• Dizziness
• Headache
• Nausea or vomiting
• Cool, moist skin
• Dark urine

Signs of heatstroke may include:

• Fever (over 104°F [40°C])
• Red, hot, dry skin
• Rapid, shallow breathing
• Rapid, weak pulse
• Irrational behavior
• Extreme confusion
• Seizure
• Loss of consciousness

As soon as you notice early signs of a heat illness, get out of the heat or sun right away. Remove extra layers of clothing. Drink water or a sports drink.

Contact your health care provider if you have signs of heat exhaustion and do not feel better 1 hour after getting away from heat and drinking fluids.

Call 911 or your local emergency number for signs of heatstroke.

Heat exhaustion; Heat cramps; Heatstroke

Buschmann JL, Buell J. Sports nutrition. In: Miller MD, Thompson SR, eds. DeLee, Drez, & Miller's Orthopaedic Sports Medicine. 5th ed. Philadelphia, PA: Elsevier; 2020:chap 25.

Centers for Disease Control and Prevention website. Heat and athletes. www.cdc.gov/extreme-heat/risk-factors/extreme-heat-and-athletes.html?CDC_AAref_Val=https://www.cdc.gov/disasters/extremeheat/athletes.html. Updated February 15, 2024. Accessed June 19, 2024.

Centers for Disease Control and Prevention website. Symptoms of heat-related illness. www.cdc.gov/extreme-heat/signs-symptoms/?CDC_AAref_Val=https://www.cdc.gov/disasters/extremeheat/warning.html. Updated February 15, 2024. Accessed June 19, 2024.

Updated by: Linda J. Vorvick, MD, Clinical Professor, Department of Family Medicine, UW Medicine, School of Medicine, University of Washington, Seattle, WA. Also reviewed by David C. Dugdale, MD, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team.