UV Radiation is Everywhere

Too much sun is dangerous. Summertime is when the sun is highest in the sky and the rays are most direct. This means that there is less filtering by the earth's thin atmosphere. You must take precautions against the sun's ultra-violet (UV) radiation.
UV radiation is a normal component of the sun's energy that in large quantities causes sunburns, and may eventually lead to premature wrinkling, skin cancer, or cataracts. Simple measures reduce risk. Here are some basics:

If your shadow is shorter than you are tall, UV levels will be high.
UV radiation is most intense between 10am and 3pm. Limit your exposure to direct sun during these hours.
Don't lay in the sun. When out for extended periods, wear a hat, along with light-colored, lightweight clothes that cover your arms, legs and the rest of your skin. Use sunglasses with UV protection and apply a sunblock.
Children need extra protection since their bodies are still developing and too much sun can be much more dangerous than to adults.
Lighter skin is more affected by UV radiation but all skin types require some type of protection.
UV radiation penetrates clouds and water so even on a cloudy day or while swimming, take precautions.
Shiny, smooth, or bright surfaces such as cement or sand can reflect UV radiation.
Cooler temperatures do not lower UV values. Skiers commonly are sunburned when they underestimate the sun's UV radiation reflected by snow.
As the UV index gets higher, use a sunscreen with a higher SPF (Sun Protection Factor) and spend less time in the sun.
If you notice blotches or other permanent changes to your skin, see your doctor.

UV INDEX NUMBER EXPOSURE LEVEL
0 - 2 Low. Color=green
3 - 5 Moderate. Color=yellow
6 - 7 High. Color=orange
8 - 10 Very High. Color=red
11+ Extreme. Color=violet

The EPA has a Sunwise Program which is great for educators and students who want to learn more.