How to Apply Sunscreen

While you're grilling, swimming, or strolling around amusement parks during those hot summer months, remember to be safe and protect yourself from the sun! Check out the tips below for choosing and applying sunscreen.
First, let's be sure you're using the right stuff!

• Select a broad spectrum sunscreen (blocks both UVA and UVB). How can you tell? Look for a 4% or higher level of one of the following: zinc oxide, micronized zinc, titanium dioxide, Parsol 1789, avobenzone.
• Choose a sunscreen with a Sun Protection Factor (SPF) rating of 30 or higher.
• Be sure that your sunscreen is appropriate for your fun-in-the-sun activity. (i.e. Waterproof for swimming, non-irritating for sports, etc.)Test it first! Make sure that it doesn't irritate your skin, but also, be sure that it's comfortable for you personally. If you can't stand a greasy feel, be sure to choose one that feels lighter. Scent is also another factor to consider.

I found it interesting what the SPF rating actually tells you. It's not the percentage of protection unto itself, but it does tell you percentage of protection against UVB (sunrays with wavelengths between 280 and 315 nm). To figure out percentage of protection, take the SPF rating, subtract 1, thendivide by the rating.
So, a sunscreen with SPF 40:

40 - 1 = 39
39 / 40 = 0.975
= approximately 98% protection against UVB rays
Now, how to apply:

• Apply sunscreen 20 minutes before going outside to allow for skin penetration/binding.
• Don't underapply! (This is the most common application mistake.) The recommended level is 2mg sunscreen per square cm of skin. (For an average adult, this means about a shot glass worth per application.)
• Reapply every 2 hours while outside until sunset. Even if "water resistant," still reapply every 40 minutes if swimming. If "very water resistant," reapply every 90 minutes if swimming.Check the expiration date! Make sure you're not using old, and therefore ineffective sunscreen.

Click this link for more great tips from http://www.sunprotection.net.