When exercising outside, sunglasses are a must. Personally, I can't stand to have the sun blinding my eyes. Not only that, but UV rays can cause cataracts and glaucoma. Two more reasons to slip on some shades. Last year, I bought a pair of expensive polarized sunglasses, thinking that "polarized" meant they blocked out those harmful UV rays.
Unfortunately, polarized lenses act as a filter to absorb light waves, which helps to reduce glare that bounces off smooth surfaces like pavement or water. This filter action is great when biking or boating but unfortunately has nothing to do with how well shades protect your eyes from UV rays. Unless the pair you wear is labeled as blocking 99 to 100 percent of UV rays (or the label may say "UV absorption up to 400nm") then all your sunglasses are doing is looking pretty. While it's possible that lenses can be both polarized and UV blockers, you can't just assume that so read the labels. If you want even more UV protection, go for wraparound sunglasses since they'll block sunlight from getting to the sides of your eyes.
Fit's Tip: When choosing sunglasses, you also want to make sure the lenses screen out 75 to 90 percent light. Try them on in front of a mirror and if you can see your eyes easily then the lenses are probably too light.