There's such a thing as waterproof sunscreen
Everything you were told as a child getting your pants pulled down playfully by a dog is a big lie: as of 2012, companies aren't allowed to put "waterproof" on their labels, says Polcari. Instead, you may see "water resistant," with a max protection time. A good rule of thumb: if you take a dip, reapply after. Note that this also applies if you're sweating it up during beach aerobics.
Sunscreen is the best way to protect yourself from the sun
Smearing on the white stuff is really just one way to keep yourself protected. Polcari also suggests hanging in the shade, wearing sun-protective clothing and swimwear, and grabbing a hat with at least a 2in brim. And remember, the sun is at its strongest between the hours of 10am and 2pm.
Sunscreen protects you from melanoma
Melanoma is still a fairly mysterious form of cancer. According to the Mayo Clinic, the exact cause isn't clear, though exposure to ultraviolet radiation certainly doesn't help. While sunscreen does play a role in helping prevent melanoma, it isn't the full answer, and families of melanoma often appear in places that don't see much sun exposure. Sunscreen does protect you from basal cell carcinoma and squamous cell carcinoma, so it's definitely still worth using. Just keep a close watch on any moles you have.