Published: Jun 17, 2014 2:41 PM EDT
Updated: Jun 17, 2014 5:51 PM EDT

Consumer Reports found 18 of 20 sunscreens tested fall below the advertised SPF on packaging.

To test, Consumer Reports applied sunscreen to panelists' backs and had them soak in a tub for 80 minutes. Then the panelists were exposed to UVA and UVB rays. 18 of the 20 came in below the SPF promised on the packaging. Two tested far below what was promised. Beyond Coastal Natural claimed an SPF of 30, but Consumer Reports' testers found it was below 15. Banana Boat Kids claimed SPF 50, but testers found it was below SPF 15.

Consumer Reports did find seven they recommend.
1. Equate Ultra Protection SPF 50, Walmart
2. Up & Up Sport SPF 50, Target
3. BullFrog Water Armor Sport InstaCool SPF 50
4. Well at Walgreens Sport SPF 50, Walgreens
5. Banana Boat Ultra Defense Max Skin Protect SPF 110
6. Coppertone Water Babies SPF 50
7. Neutrogena Ultimate Sports SPF 70

Below is a list of tips on applying sunscreen from the American Academy of Dermatology:

Use enough sunscreen to generously coat all skin that will be not be covered by clothing. Ask yourself, “Will my face, ears, arms, or hands be covered by clothing?” If not, apply sunscreen. Most people only apply 25-50 percent of the recommended amount of sunscreen. Follow the guideline of “one ounce, enough to fill a shot glass”, which dermatologists consider the amount needed to cover the exposed areas of the body.

Adjust the amount of sunscreen applied depending on your body size.

Apply the sunscreen to dry skin 15 minutes BEFORE going outdoors.

Skin cancer also can form on the lips. To protect your lips, apply a lip balm or lipstick that contains sunscreen with an SPF of 30 or higher.

Re-apply sunscreen approximately every two hours or after swimming or sweating heavily according to the directions on the bottle.