When the heat index is high, it's best to stay in an air-conditioned environment. If you must go outdoors, you can prevent heat exhaustion by taking these steps:
Use a sunscreen with a sun protection factor (SPF) of 30 or more.
Take additional precautions when exercising or working outdoors.The general recommendation is to drink 24 ounces of fluid two hours before exercise, and consider adding another eight ounces of water or sports drink right before exercise. During exercise, you should consume another 8 ounces of water every 20 minutes even if you don't feel thirsty.
Avoid fluids containing either caffeine or alcohol, because both substances can make you lose more fluids and worsen heat exhaustion. If you have epilepsy or heart, kidney, or liver disease; are on fluid-restricted diets; or have a problem with fluid retention, check with your doctor before increasing liquid intake.