Why Your Sunscreen May Not be Protecting You
What to wear, how much to put on and when to put it on. It's a lot to think about.

Virginia Mason's Dr. Renata Jenkin says think about this: There are three kinds of ultra-violet rays. UV-C: which is blocked by our ozone layer.

"Which is a good thing because it would fry us all," adds Jenkin, who is a long-time dermatologist.

UVB is the primary cancer-causer. UVA make you tan, but doctors now know it can give you cancer too.

Dr. Jenkin says just UVA-UVB coverage is still not enough. Make sure there's an ingredient called Avobenzone.

"It's the Avobenzone that gives us the wide spectrum of protection," she says.

And, she says you must apply least 20 minutes before you head out.

"Because it is a drug, and like any drug it has to become activated."

"And it can break down," says Jenkin, "So re-apply every 3-4 hours or even sooner if your sweating or in the water.

Also: look for a newer ingredient called Helioplex which makes your sunscreen last longer. Instead the 3-4 hours:

"...you can get 7-8 hours," says Jenkin.

Dermatologists say if it's light out, you're still soaking in cancer causing rays and UVA rays cut right through glass so you need protection even sitting in a car.

When it comes to makeup:

"By lunch time that is degraded," explains Jenkin.

She warns layering on SPF 15 lotion, moisturizer and makeup doesn't mean you're better protected. It's still just 15, and it all still wears off--no matter how you look.

"You're makeup is still on, but the chemical that allows the protection has now degraded," says Jenkin.

Important advice, when it's nearly impossible to avoid the sun.

"There's no such thing as 100 percent protection."

Here's another note: SPF 15 offers about 93% protection. SPF 30, offers just a bit more, at 95% - not double. So, Dr. Jenkin emphasizes: just make sure to apply enough sunscreen- and do it often.