1. You don't apply enough.
Shots, shots, shots, shots! Break out that shot glass from your liquor cabinet and take a good, hard look. That's the amount you need to be applying to your body—yes, your entire body. And don't forget your face. That pretty mug of yours only requires about a nickel amount. If you use less, it doesn't *necessarily* mean you'll burn, but it does mean you're not getting all the benefits labeled on that SPF bottle of yours. So just give your body the drink it needs, okay?
2. You skimp on reapplying.
Doing it once is not enough. You need to reapply the same amount as above after you take a dip, excessively sweat, or if it's been more than two hours since you've applied. And quick heads up: "Water resistant" is not the same thing at "waterproof." You still have to reapply after you hit the water. (Sorry.)
3. You buy the wrong SPF.
SPF is the amount of UVB rays you're protected against, AKA the rays that cause your skin to burn. It is not the amount of UVA rays you're protected against, AKA the rays that are responsible for aging. (Meaning you still need to try to stay out of direct sunlight as much as you can.) Also, no, the SPF number does not correlate to how much your sunscreen is protecting you. A sunscreen with SPF 100 doesn't block out 100 percent of the rays—only about 98 percent, while a lotion with SPF 30 will protect you against roughly 95 percent of rays. And no sunscreen offers full protection. (Whomp, whomp.) Always look for a broad spectrum sunscreen, which guards against both types of sun rays. (And yes, both rays can cause cancer.)
4. You don't rub in sprays.
Sprays are much easier to apply and less odorous. The downside, however, is that you're more likely to forget places and have uneven coverage. (Thank a lot, spray.) To make sure you're getting the coverage you need, spray continuously on a specific part for about five seconds and then rub it in and out. Holding the nozzle down for that period of time allows for more even distribution while rubbing ensures you don't miss a uncovered surface.
5. You, um, don't use it at all.
Do you have a year-round tan thanks to the parents? Doesn't matter. Your skin color doesn't affect which kind of SPF you should be using—everyone should be looking for the same thing. The American Academy of Dermatology recommends all people (regardless of skin tone) should apply at least an SPF 30 to any exposed body part.
6. You don't apply it when you know you're going to be inside.
Windows! WINDOWS. Those glass panes allow rays to reach your skin, so it's still important to protect yourself even if you aren't spending hours outside. And don't forget car time. Drivers should keep SPF handy, as UV rays penetrate the glass and often affect only one side of your body, meaning while you'll only have half the risks, you'll have all the embarrassment of a one-sided farmer's tan. And office settings aren't particularly safe either— skin discoloration can occur just from light emitted from computers, workplace lighting, and cell phone light.
7. You don't put sunscreen underneath your clothes.
Guess what? A white tee shirt only has an SPF 3. And that number drops if it gets wet. Ugh. Do NOT neglect putting the white stuff on every inch of you body, even if it'll be covered by an article of clothing—bikini, sunglasses, hat...you get the gist.
8. You forget certain body parts.
Major biggies: the scalp, ears, eyelids, lips, and the tops of feet. If you hate goop in your hair, opt for a spray that dries quickly—yes, they exist. Tip: Don't forget your hair part. It's the most exposed area of your head, and skin cancers in the scalp are often diagnosed much later—meaning it'll likely have progressed and be more aggressive when it's finally detected. For easier application to your eyelids, ears, and lips, try testing out a sunscreen stick.
Sources: Mona Gohara, M.D., board-certified dermatologist in Connecticut; Dendy Engelman, M.D., dermatologist at Manhattan Dermatology and Cosmetic Surgery.