Sunscreen, By the Numbers

Sunscreen numbers, what do they mean?

Sun Protection Factor , or SPF is a measure of how effectively a particular sunscreen limits
UVB ray exposure to the skin. This is the number printed on the front of your sun screen

The SPF number refers to how long you can stay in the sun, not how strong the product is.

SPF 30 is not twice as strong as SPF 15, it only means that you can stay in the sun twice as long, when applied appropriately.

For example, if your skin normally begins to burn in 10 minutes of mid-day sun, if you were
wearing an appropriate amount of SPF 15 you would be able to stay in the sun 10 min X 15, or 150 minutes before you begin to burn.

If you are wearing SPF 30, you are not twice as protected, it only means you can stay in the sun twice as long as you could with SPF 15.

Keep in mind that the SPF studies are done with generous amounts of sunscreen applied. As a general rule, one ounce (approximately one large handful of sunscreen) is necessary to cover the entire body.

Be aware that activities such as swimming, exercising, and taking clothes on and off may
decrease the effectiveness of your sunscreen and you many need to reapply for proper

An appropriate amount of SPF 15 will provide approximately 2 hours of protection from UVB rays while an appropriate amount of SPF 50 will provide approximately 8 hours of protection. Of course, if you are performing any activity in which the sunscreen may be compromised, please reapply for appropriate protection.


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