Exposure to high temperatures, particularly when combined with high humidity and strenuous physical activity can lead to heat exhaustion and heat stroke. Fortunately, heat exhaustion is preventable, says Dr. Michael Raymond Watts, an Emergency Physician at Lee's Summit Medical Center. He says it's important for people working or playing outdoors to drink plenty of water to avoid becoming dehydrated and to wear lightweight, light-colored clothing. Here's what else you need to know.