No product on the market today totally blocks the sun's rays. It's more accurate to call the stuff "sunscreen".
It's more likely "water resistant," taking up to 80 minutes to wash off. If you're a permanent fixture in the pool, or tend to get sweaty, reapply often.
A bottle with broad spectrum protection will put up a good fight against both UVB and the more harmful UVA rays.
The sun protection factor (SPF) gives you an indication of how long it will take the sun's rays to cause UVB-induced redness. The higher the number, the longer you're protected. But note: SPF doesn't measure protection from UVA. Bottom line: sun responsibly. "Don't use sunscreen as a replacement for common sense," says Dr. Vince Bertucci, dermatologist at Bertucci MedSpa Inc. in Woodbridge, ON. "A sunscreen with SPF 30 isn't a licence to stay in the sun 30 times longer."
Chemical ingredients protect the skin by absorbing UV radiation. Some (homosalate, octinoxate and octisalate) shield you from UVB rays, and others (Parsol 1789, Mexoryl SX and Mexoryl XL) from UVA. Many products contain a combination.
Titanium dioxide, zinc oxide
Titanium dioxide and zinc oxide are tiny metal particles that reflect and scatter UV light. They’re not chemical sunscreens and won't penetrate your skin, so they're ideal for kids or anyone with sensitive skin. The downside: they may make your skin look whitish.
You're not so likely to find PABA, or para-aminobenzoic acid, in your sunscreen these days. This ingredient was found to cause allergic skin reactions typically consisting of redness and irritation in some folks, so many manufacturers avoid it now.
Fruit and nut extracts
Essence of mango may make you smell good, but it hasn't been proven to block the sun. And fruit or nut ingredients can lead to allergic reactions in some people.
Sunscreen ingredients break down over time – possibly sooner if the sunscreen has been stored in a hot place, says Bertucci. "Sunscreens are often kept in the glove compartment or a beach bag."