Give a summary of the guidelines for using sunscreen to prevent overexposure.

Answer:

Be sure to buy sunscreen of at least 15 SPF and apply it to all areas of the skin that will be exposed to sunlight at least 20 minutes before going outside. Generally, sunscreen should be reapplied every 2 hours. If you exercise moderately, sweat, or swim during that time, you should reapply more often.