With summer in full swing, you’re probably outside more than usual. And chances are it feels hot out there, particularly when you’re exerting yourself.

Most of the time, your body is quite good at regulating its internal temperature. “The body’s main way that it cools itself is through sweat,” says Michelle Cleary, Ph.D., associate dean of graduate programs at Chapman University, in Orange, Calif. 

But if you aren’t drinking enough to keep up with the fluid lost in sweat, your body can heat up too much and become dehydrated. 

When you're physically active under these conditions, you can feel lethargic and uncomfortable, but in some cases, you can actually become dangerously sick.  A 2011 study found that playing sports, exercising, and doing yard work were among the most common causes of heat-related emergency room visits.

But you don’t have to stay inside this summer to stay safe. These best practices will help keep you from overheating during your summer workouts.

Dress Right and Safeguard Your Skin

What you wear can help keep you cooler when you’re exercising or working outdoors.

“You want to avoid anything that traps moisture against your skin,” Cleary says. Opt for lightweight, loose-fitting items, which allow sweat to evaporate more easily. Also, stick with light colors, which absorb less heat than dark ones. Moisture-wicking polyesters may help move sweat away from your skin, where it can evaporate and cool you down.

Protect yourself from the sun’s rays, too, by wearing sunscreen with an SPF of 40 or higher (check our sunscreen ratings for best brands) during your outdoor summer workouts. Apply it at least 15 minutes before you go outside, and reapply at least every two hours.

Not only does sunburn raise your risk of skin cancer, but, according to Luke Pryor, Ph.D., professor of kinesiology at California State University, Fresno, it can hamper your body’s ability to cool itself by damaging your sweat glands.

Stay Hydrated

Your body is about 60 percent water, which allows your kidneys to filter out waste and your blood to transport nutrients throughout your system. Your sweat mechanism also helps keeps your body at the right temperature, between 97 and 99 degrees Fahrenheit.

How much water do you need? The Institute of Medicine recommends that men consume 3.7 liters of water daily and women 2.7 liters (from food and non-alcoholic beverages). 

Instead of trying to keep track of your liters, Sarah Fowkes Godek, Ph.D., director of the HEAT Institute at West Chester University of Pennsylvania, recommends that you rely on your sense of thirst to tell you how much water to drink.

“Our thirst mechanism is adequate and very well developed,” Fowkes Godek says. The exception is older adults. Your sense of thirst diminishes as you age, so relying on thirst for seniors may not be sufficient to keep them hydrated. See our advice for older adults here.

As for what to drink, water is best, says Fowkes Godek. While you do lose important nutrients known as electrolytes —such as sodium, magnesium and potassium—when you sweat, she says most people have no need for sports drinks or other beverages fortified with electrolytes. Most people get enough nutrients from meals and snacks to replace what they lose, and sports drinks often contain a lot of added sugars.

The exceptions: People who work out for more than an hour at a time, and workers who labor for long hours outside in the heat may need to replace electrolytes.

Consuming water-rich foods like melon, citrus, and leafy greens can also help keep you hydrated. And while the heat may blunt your appetite, try to have a small snack of about 150 to 200 calories an hour to 30 minutes ahead of your workout—if you haven’t had a meal within the prior four hours. Refuel within an hour afterward. (See our advice on what foods are best to eat before and after any workout.)

Time Your Activity Right

During the summer, do as much of your outdoor physical activity in the morning or evening, when it’s slightly cooler. When outside, stay in the shade as much as possible.

It’s also important to let your body acclimate to exercising or working in the heat, says Douglas Casa, Ph.D., CEO of the University of Connecticut's Korey Stringer Institute, which produces research and advice on the prevention of heat-related deaths for athletes and workers. 

That means, ideally, slowly working up to a full intensity training session or work day. A 2016 analysis found that taking eight to 14 days to acclimatize to exercising or working in the heat may be most effective for minimizing heat stress to your body. But that's not always practical. Still, if you have an outdoor activity such as a big hiking trip, long-distance run, or a major yard project planned, try to work up to it over a period of days.

Adults who supervise groups of children, at camps or in sports teams, for instance, should make sure they give youngsters a chance to adapt to the heat as well. See tips from the American Academy of Pediatrics on how to keep youngsters safe in the heat.  

Watch Out for the Symptoms of Heat Stroke

If you notice any signs of dehydration or heat-related illness—including dizziness or lightheadedness, headache, fatigue, nausea or vomiting, and muscle cramps—take a break from your activity, find shade or a cool room, and drink water.

And note that while the ability to cope with heat and humidity do vary from person to person, some weather conditions merit precautions for all. So, pay attention to heat watches, advisories, and warnings in your area (available through the National Weather Service). On days with these alerts, take extra care to stay hydrated, and consider modifying your activity level or moving your summer workout indoors for the day.

And be on the lookout for signs of heat stroke, which can be fatal if not addressed quickly. The two most important symptoms are body temperature above 104 degrees and central nervous system problems such as losing consciousness, irritable or irrational behavior, mood changes, and disorientation.

You may not have a thermometer on hand, but if you experience one or more of the behavioral symptoms mentioned above during a summer workout, or notice them in someone else, take action: “Get body temperature down as fast as humanly possible,” says Casa at the University of Connecticut.

Move out of the heat and direct sun, and into a cold bath or shower (or use water from the garden hose or any other water that’s available if you can’t get indoors). Flip on a fan or air conditioning to speed cooling. After taking action to cool the person down, call 911.