Guide to sunscreen use:
1. Look for labels that say "broad spectrum" or UVA and UVB protection. Zinc oxide and titanium dioxide are good ingredients for sun protection (Of course, I like the natural brands without all those weird ingredients and parabens and junk---but zinc oxide seems ok for now).
2. Wear at least SPF 15 anyday you will be outside for more than 20 minutes (even on non-sunny days because up to 80 percent of UV rays can penetrate clouds).
3. Apply sunscreen 15 minutes before you go outside and re-apply every 2 hours (even at SPF 60--it starts to breakdown when exposed to rays).
4. Use a shot glass size amount of sunscreen for each application and cover all exposed skin--even the tops of ears and tips of toes---consider wearing a hat to protect your scalp!
5. Re-apply waterproof sunscreen when you get out of the water---it's not really waterproof, just resistant and it leaves uneven protection after you've gotten it wet.
6. Sunscreen has a pretty stable shelf life, but doesn't last more than 3 years (or the exp date, whichever is first)---and will not last as long if you leave it in the car or other extreme temperature exposures. If it separates, changes color, or smells weird, junk it.
Please note: This information is for adults. Children and sunscreen are a whole different story...