Summer is a favorite time of year for many Minnesotans who like to get outside and enjoy sports, boating, fishing, camping, hiking, gardening and many other activities that can be done outdoors. It’s great to enjoy the season. But when outside, it’s important to remember one thing: sunscreen.

Sunscreen is designed to prevent sunburn and protect against premature aging and skin cancer. Skin cancer is the most common form of cancer in the United States. More than one million cases are diagnosed every year.

How does the sun damage skin? Through ultraviolet radiation, or UVR. UVR is made up of ultraviolet A (UVA) and ultraviolet B (UVB) rays. When UVR reaches human skin it is absorbed and interacts on the molecular level with proteins, lipids and cellular DNA. It is the damage to the DNA cells that can eventually lead to the development of skin cancer.

Sunscreen works by absorbing or reflecting these damaging rays before they have a chance to interact with the skin. How well a sunscreen protects against the effects of UVB rays is the basis for the standard measurement of its potency. This is known as the “sun protection factor” or SPF. There isn’t an FDA-approved measurement for the sun’s ability to block UVA rays, but when shopping for sunscreen, choose one that is “broad spectrum,” meaning it blocks both UVB and UVA rays.

The number of an SPF indicates how many times longer it will take to produce a sunburn when protected versus unprotected. For instance, if a fair-skinned person would be burned in 10 minutes without any sunscreen, an SPF of 15 would allow her to be in the sun for 15 times that, or 150 minutes. An SPF of 30 would allow for 300 minutes, and so on.

When correctly applied, a sunscreen with a SPF of 15 reduces UVB exposure to about seven percent of its original value. Not all sunscreen is “correctly applied” however. In order to be effective, sunscreen should be applied about 30 minutes before exposure to the sun, and then reapplied every two hours while in the sun -- more often if in the water. Water-resistant varieties of sunscreen wear off after about 40 minutes in the water. Waterproof types wear off after about 90 minutes. And remember, sunscreen can rub off on beach towels. Reapply after drying off after a swim. Sunburn can occur when people don’t use enough sunscreen. About one ounce is the amount needed to cover the exposed areas of the body. Apply liberally wherever skin isn’t covered by clothing. And don’t forget tops of ears, lips, tops of feet and the top of your head if it isn’t covered with hair.

Sunscreen use is especially important for children. It is estimated that 60 to 80 percent of total lifetime sun exposure occurs in the first 18 years of life. And a number of studies have confirmed that repeated sunburns substantially increase the risk of melanoma -- skin cancer. Children who repeatedly get sunburned while young have a greater risk of developing skin cancer later in life.

When it comes to kids (and adults as well), sunscreens aren’t just for the beach. Make it a habit to apply sunscreen every day before your child goes out to play -- even on cloudy days when 80 percent of the damaging rays get past the clouds. Sunscreens designated for “kids” typically are less irritating to the skin and eyes. Even so, apply sunscreen very carefully around the eyes.

Sunscreens come in many forms, but they aren’t the only way to protect yourself against the sun. Avoid exposure, especially during the sun’s peak hours between 10:00 a.m. and 2:00 p.m. each day. Wear sunglasses to protect your eyes. It’s been shown that the wrap-around style of sunglasses can block 99 percent of UVA and UVB rays. Wear a large brimmed hat to shade your face. Stay in the shade -- a thick tree can offer an SPF of about 15; a canopy of trees gives an SPF of about 30.

If you do happen to overdo it in the sun, take a cool bath or use cool compresses on the sunburned areas. Take acetaminophen or ibuprofen for discomfort, following dosage instructions on the bottle. Apply a topical moisturizer or aloe gel to sunburned areas. If blisters are present, do not break them open because this can lead to infection. Stay out of the sun until the skin has healed completely.

If you or your child develops blisters or shows symptoms of heat stress such as fever, chills, nausea, vomiting or lightheadedness, contact your primary care physician.

Summer is a great time to enjoy the great out of doors -- as long as you do it in a safe, skin-healthy way -- with lots of sunscreen!

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Dr. Rogers is a board certified family practice physician at Raiter Clinic in Cloquet.