Consumer reports tested 34 sunscreens and found that 11 products did not deliver their promised SPF protection.

They were off by 16 to 70 percent. It doesn't mean that sunscreens aren't helping, but you may not be getting the protection that you think.

The study focused on how sunscreens hold up in water. Dermatologists recommend using a broad spectrum sunscreen with an SPF of 30 or more and reapplying frequently.

Among consumer reports the top sunscreens that met their SPF claims:

La Roche-Posay SPF 60
Vichy Capital Soleil SPF 50
Coppertone Water Babies SPF 50
Walmart's Equate Ultra Protection SPF 50
No-Ad Sport SPF 50
Banana Boat Suncomfort SPF 50

Remember, sunscreens don't have to be expensive to be effective.