Washington Master Esthetics Practice Exam

If skin develops erythema with 10 minutes of sun exposure, and the SPF of the sunscreen is 15, how long is the skin protected?

1. 100 minutes

2. 120 minutes

3. 150 minutes

4. 180 minutes

The correct answer is: 150 minutes

To determine how long the skin is protected by a sunscreen with an SPF of 15, it's essential to understand what SPF represents. SPF, or Sun Protection Factor, indicates how much longer a person can be in the sun without getting sunburned compared to being without sunscreen. In this case, if the skin starts to develop erythema (redness) with just 10 minutes of sun exposure when no sunscreen is applied, applying an SPF 15 means the person can theoretically stay in the sun for 15 times longer without experiencing the same level of sunburn. Therefore, to calculate the protection duration, you would multiply the time taken to burn (10 minutes) by the SPF value (15). So, 10 minutes multiplied by 15 equals 150 minutes of protection. This calculation demonstrates why the correct answer is that the skin is protected for 150 minutes when using an SPF 15 sunscreen. Understanding this allows for proper sun safety practices and reevaluates how often one should reapply sunscreen, as effectiveness can diminish over time depending on factors like sweating or water exposure.