Summer is prime time for outdoor activities, but sometimes heat and physical activity can combine in a dangerous way, causing heat exhaustion or heat stroke.

Blake Boggess, DO, of Duke Sports Medicine, explains the difference between several heat-related illnesses and how to recognize and prevent them.

“There is a whole spectrum of heat illnesses that range from dehydration to exercise-associated muscle cramps, and may progress to heat syncope, or fainting,” Boggess said. While fainting can be frightening, a little rest is often all that is needed to recover before returning to your normal activities.

Exercising in hot and humid weather can also cause heat exhaustion or heat stroke, which are more concerning conditions.

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Heat Exhaustion

“Heat exhaustion occurs when there is an inability to continue exercising that could be from a combination of heavy sweating, dehydration, sodium loss, and energy depletion,” Boggess said.

Someone suffering from heat exhaustion may experience muscle cramps and weakness, headache, dizziness, hyperventilation, and nausea. They will have a temperature between 97 and 104 degrees.

Resting and cooling off in the shade are recommended to recover from heat exhaustion. Drinking sports drinks may also help, as they help replenish salt and other minerals while rehydrating the body.

Heat Stroke

Heat stroke is more dangerous than heat exhaustion and happens when a person’s body temperature rises above 104 degrees. Heat stroke can cause neurological changes, such as confusion or difficulty speaking and moving, and may be life threatening if not treated.

Symptoms of heat stroke may include low blood pressure, hyperventilation, altered mental state, seizures, and coma.

While people usually recover fully from heat stroke, the danger of long-lasting damage increases the longer a person’s body temperature is above 104 degrees. If you suspect someone is suffering from heat-related illness, it’s important to get an accurate temperature and try to cool him or her down with ice, cool cloths, or fans.

If you are outside, move the person to a shady area. “Treat them by removing excess clothing to increase the evaporative surface and to facilitate cooling,” Boggess said.

If you notice any changes in the person’s brain functioning, such as confusion or memory loss, or if their temperature is above 104 degrees, seek emergency medical attention immediately.

Prevention Is the Best Medicine

When you are physically active, your body loses a lot of water through perspiration and breathing. Replenishing that water is vital to keep your internal systems functioning properly and help regulate body temperature.

It’s also a good idea to prepare your body to withstand high temperatures before doing anything physically active.

“Individuals can adapt to exercising in the heat through a progressive increase in intensity and duration of workup and heat,” Boggess said.

By acclimating your body over a period of 10 to 14 days, you can lower your risk of heat exhaustion or heat stroke and improve your ability to safely enjoy physical activity even when the summer sun is beating down and the humidity index is high.