teratologist darryl regal says the 11 is the one you'll actually use. >> praise are the most common type of sunscreen. the issue with spray, sometimes hard to know where you miss. so-so we recommend you put two coats on. >> american ahmaddiya add any of dermatology, says look for spf broad spectrum of 30 or higher. most last about three years. >> sunscreen is not required to is expiration dates on it, but what breaks sunscreen down is extreme heat. so if you live it in your car. that will break the sunscreen down. >> most people don't use enough sunscreen, and don't reply as often as they should. experts say, a shot glass full will cover the whole body. and row apply every two hours. even if you have darker skin, you're still at risk for skin cancer. and it is never too late to protect yourself, even if you got too much sun as a kid. >> the damage you get from the sun is cumulative. there is sort after meter running on your skin. that really never goes backward, but if you can slow the meter down. >> you could improve your risk later on. marlie hall, cbs-3, "eyewitness news". >> coming u