You’ll find this on your bottle or tube of sunscreen, and may have wondered what it stood for along with the associated number. SPF is an abbreviation for Sun Protection Factor, and the number associated with it is known as the amount of time measured for the sunscreen’s effectiveness.6,13

So if you are using an SPF of 15, you are protected from sunburn 15 times longer than the time it usually takes for your skin to turn red in the sun without sunscreen, so if you normally burn in 20 minutes without sunscreen, then wearing SPF 15 sunscreen theoretically lets you stay in the sun for approximately 300 minutes without burning.10,13

It is highly recommended that you apply at least SPF 15 at 2 hour intervals and that you should apply as much as one ounce (about a shot glass full) to your entire body.1,6,10,14,15

The American Skin Cancer Foundation states that SPF ratings do not however offer 100% protection from the sun, but rather SPF 15 protects you from 93% of harmful UVB rays, SPF 30 protects you from 97%, while SPF 50 protects you from up to 98% of the UVB rays.10,13

For the highest amount of protection, it is best to use a broad spectrum or full-spectrum sunscreen that protects your skin from both UVA and UVB rays.6,8,11,12,13