Nothing ages skin faster than sun damage. Using sunscreen is the easy, obvious solution.
Proper sunscreen use can prevent not only wrinkles and lines, but also skin cancer, especially melanoma. This year the deadly disease will strike nearly 140,000 people in the United States, killing nearly 10,000. It’s the most common form of cancer for young adults (age 25 to 29) and the second-most common for those aged 15 to 29 years old. 
But what you don’t know about sunscreen really can hurt you.
Here are three little-known sunscreen facts that can (literally!) save your skin this summer.
1.You’re Not Using Enough
You applied sunscreen this morning. Now you’re set for the day, right?
“Everyone reading this is probably using too little and applying too infrequently. More is better. Trust me, you’ll thank yourself later,” says Talia Emery, MD, medical director of Remedy, a cosmetic dermatology center in Westlake Village, California.
“No matter which SPF you use, sunscreen should be reapplied every two hours and immediately after swimming or sweating.”
The American Academy of Dermatology suggests you generously coat exposed skin 15 minutes before going outdoors, using “enough to fill a shot glass.”
2.They’re Not Created Equal
The most common sunscreens are chemical-based formulations, containing ingredients that absorb the sun’s rays.
Sunscreen may also be mineral-based**,** containing zinc oxide and titanium dioxide. These deflect ultraviolet rays away from the skin. Mineral sunscreens are less likely to sting your eyes; they are gentler to skin; and they block both UVA and UVB rays.
“Mineral sunscreens are the most trustworthy. They are the most stable [i.e., don’t degrade as quickly on your skin or in the bottle] and provide the broadest protection,” says California dermatologist Cynthia Bailey, MD, whose blog (drbaileyskincare.com) covers sun protection.
In addition to the messy white goo that we all love to hate, you can find sunscreens in sprays, wipe-on sheets, powders, roll-ons, and waxy sticks.
And many sunscreens do double-duty as beauty products. “Moisturizing, anti-aging, medicated, tinted, acne preventative, makeup priming, and other all-in-one SPF-30+ sunscreens are evolving, so one beauty product treats a variety of needs,” says esthetician Naomi Fenlin, owner of About Face Skin Care in Philadelphia.
Some sunscreens also contain antioxidants such as Vitamin C and green tea, or plant-based ingredients such as aloe vera or avocado butter, for a protective boost.
3.30 is Not Twice as Much as 15
Sun Protection Factor (SPF) 15 sunscreen blocks about 93 percent of UVB rays, compared to SPF 30, which blocks 97 percent. SPF 50 protects against 98 percent of UVB rays.
Many dermatologists recommend SPF 30. “The payoff above SPF 30 is negligible,” says Minneapolis dermatologist Charles Crutchfield III, MD.
But SPF measures only UVB rays — not UVA rays, so be sure to choose a broad-spectrum sunscreen that protects from both types of the sun’s skin-damaging ultraviolet radiation.
“UVB refers to the burning rays. UVA are the aging rays that cause brown spots and penetrate deeply into the skin. UVA rays are also linked to skin cancer,” says Chicago dermatologist Carolyn Jacob, MD.
For additional information about sunscreen on AWomansHealth, see:
 Skin Cancer. American Academy of Dermatology website. Available at . Accessed February 5, 2015.
 Sunscreen FAQs. American Academy of Dermatology website. Available at . Accessed March 30, 2015.
 Sunscreens Explained. Skin Cancer Foundation website. Available at . Accessed March 30, 2015.