Going in the sun this summer? This article is a must read. Paula Begoun from 
The Cosmetics Cop writes about how to find your perfect SPF number. It's pretty lengthy, so grab a cup of coffee and enjoy!
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The BasicsSun protection is an everyday must for anyone concerned with keeping their skin in top shape (and that includes avoiding wrinkles, brown discolorations, building collagen, keeping skin firm, and even preventing skin cancer). SPF 15 is the minimum rating to look for and greater is better for some skin colors and conditions; all sunscreens must be liberally applied; and UVA protection is critical.
UVA protection depends on the active ingredients in the product you are using so be sure one or more of these active ingredients are included: avobenzone (sometimes listed as butyl methoxydibenzoylmethane), titanium dioxide, zinc oxide, Mexoryl (ecamsule) or, outside the U.S., Tinosorb.   
Decisions, Decisions
There are several important factors that influence how you choose and should apply a sunscreen: 
  - How long you are going to be in the sun or      sitting next to a window (UVA radiation, the sun's most damaging rays,      come through windows). The longer you are going to be in the sun or      exposed to UVA radiation via windows the higher the SPF number you need to      look for. 
- Are you willing to apply your chosen sunscreen      liberally? No matter what SPF rating you choose, you have to apply it      liberally. If you aren't applying it liberally always go for a higher      number to assure you are getting as much sunscreen ingredients on your      skin as possible.
- Will you be swimming or perspiring heavily? If      so, go for sunscreens labeled water resistant or very water resistant. Be      sure to reapply as directed, especially after toweling off.
You'll also want to take into consideration your skin type and whether or not you'll be wearing makeup. 
  - Those with normal to dry skin should use      sunscreens in a lotion or cream base.
- Those with oily or combination skin should go for      sunscreens formulated in a lightweight lotion with a matte finish, a      liquid, or an alcohol-free gel base. Many spray-on sunscreens are      excellent for oily skin.
- If you're going to be wearing foundation, you can      choose a foundation with sunscreen and pair it with a moisturizer with      sunscreen and a pressed powder with sunscreen!
What's Your Rating?Your ideal SPF number is a multiplication figure based on your skin color and the SPF number on the product.

REGARDLESS OF YOUR SKIN COLOR AND HOW EASILY YOU TAN, WRINKLES, SKIN DISCOLORATIONS, AND SKIN CANCERS ARE PRIMARILY CAUSED BY UNPROTECTED SUN EXPOSURE! 
  Next, Do the Math: 
  - Your Level of Sunburn Risk x by the SPF Rating =      Safe Sun Exposure for Your Skin Color
- The SPF number is a rating that determines how      long you can stay in the sun without burning when you wear that product      without needing to reapply it. It does not indicate quality of protection,      just length of time. Here's how to do the math. If you have:
- Level 1 skin (very fair): That means       you usually get a burn in about 15 to 20 minutes of unprotected sun       exposure. Determining your skin's response to various SPF ratings works       like this: 
- SPF 15 x 20 minutes = 300 minutes (5        hours) of protection
- SPF 30 x 20 minutes = 600 minutes (10        hours) of protection
- SPF 45 x 20 minutes = 900 minutes (15        hours) of protection
- Level 2 skin (fair to light): That       means you usually get a burn in about 30 minutes of unprotected sun       exposure. Determining your skin's response to various SPF ratings works       like this: 
- SPF 15 x 30 minutes = 450 minutes (7.5        hours) of protection
- SPF 30 x 30 minutes = 900 minutes (15        hours) of protection
- SPF 45 x 30 minutes = 1,350 minutes (22.5        hours) of protection
- Level 3 skin (light to medium/olive):       That means you usually get a burn in about 40 minutes of unprotected sun       exposure. Determining your skin's response to various SPF ratings works       like this: 
- SPF 15 x 40 minutes = 600 minutes (10        hours) of protection
- SPF 30 x 40 minutes = 1,200 minutes (20        hours) of protection
- SPF 45 x 40 minutes = 1,800 minutes (30        hours) of protection
- Level 4 skin (medium to tan): That       means you usually get a burn in about 60 minutes of unprotected sun       exposure. Determining your skin's response to various SPF ratings works       like this: 
- SPF 15 x 60 minutes = 900 minutes (15        hours) of protection
- SPF 30 x 60 minutes = 1,800 minutes (30        hours) of protection
- SPF 45 x 60 minutes = 2,700 minutes (45        hours) of protection
- Level 5 and Level 6 skin (brown to dark       brown or black): That means you usually get a burn in about 120       minutes (2 hours) of unprotected sun exposure. Determining your skin's       response to various SPF ratings works like this: 
- SPF 15 x 120 minutes = 1.800 minutes (*30        hours) of protection
- SPF 30 x 120 minutes = 3,600 minutes (60        hours) of protection
- SPF 45 x 120 minutes = 5,400 minutes (90        hours) of protection
  *Note that level 5 and 6 skin should do just fine with a well-formulated sunscreen rated SPF 15. However, liberal applications is still important. If you do not think you'll be applying the sunscreen as liberally as you should, consider a sunscreen rated SPF 30.
