Exercising outdoors is part of the joy of summer, but as temperatures and humidity soar, smart exercisers are careful to take precautions so the heat doesn't get the best of them or their workout. Picking your time to exercise is crucial, said Richard Cotton, a spokesman for the American Council on Exercise, in San Diego. "When it's very hot and very humid, it's best to exercise in the cooler times of the day, morning or evening, or not at all," added Cotton, chief exercise physiologist with MyExercisePlan.com, a customized Web-based program. Skipping a day now and then might be wiser than falling victim to heat illnesses, which can occur when the body's cooling mechanism becomes overloaded. The risk for heat illness rises with the temperature and humidity. Heat exhaustion, the milder form of heat-related illness, is marked by flushed or pale skin, muscle cramps, heavy perspiring, nausea with or without vomiting, and headache. Heat stroke, a more serious problem, is life-threatening and occurs when the body cannot regulate its temperature. Heat stroke onset can occur within 10 or 15 minutes of first symptoms, which include a very high body temperature -- over 103 degrees Fahrenheit -- hot or dry red skin, absence of sweating, nausea, dizziness and disorientation. Loss of consciousness can follow. To treat heat exhaustion, the federal Centers for Disease Control and Prevention recommends resting and taking a cool shower, bath or sponge bath. Your physician may also recommend drinking cool, nonalcoholic beverages. Heat stroke requires immediate medical assistance and immediate cooling of the victim. The CDC recommends getting the affected person to a shady area and cooling them however you can until help arrives. This might include immersing the person in a tub of cool water or placing them in a cool shower. Monitor body temperature and keep up the cooling process until body temperature drops to 101 or 102 degrees F. Muscle spasms may set in during heat stroke. If this happens, the CDC advises that individuals aiding a heat-stroke victim find ways to keep them from injuring themselves. However, caregivers should not place objects in the victim's mouth or provide them with fluids at this point. Staying hydrated can help you stay healthy in the heat and minimize the changes of heat exhaustion or heat stroke. Physical activity in hot weather triggers a surprisingly high level of fluid loss via sweating, said Fabio Comana, a certified personal trainer and the certification and exam development manager at the American Council on Exercise. "The human body can sweat off, if someone is in good shape, up to 3 liters an hour," Comana said. For someone not in top shape, the loss can still be up to 2 liters an hour, he said. Drink water before and during workouts, Comana and Cotton suggest. About 20 minutes to an hour before exercise, drink at least 8 ounces or even 16 ounces. During exercise, drink every 15 minutes or so, 6 to 8 ounces, suggests the American Council on Exercise. Wear suitable workout wear, Comana and Cotton suggest. "Wear light colors to reflect heat," Cotton said. "It's best to shade your head as comfortably as possible." And the new wicking material for shorts and shirts do make a difference, Cotton said. If you find yourself overheating and don't have wicking material workout wear on, Comana said just wetting a cotton shirt will help you cool off. "It will lose about 90 percent of its insulation properties," he said. "It's an effective way to get rid of the heat."