Q: With summer upon us, I have started to apply sunscreen. What does the SPF rating mean (e.g. SPF 30)?
A: Not only are we well into summer, but May was also Skin Cancer Awareness Month. So, it is a great time to understand the sunscreen ratings.
SPF stands for Sun Protection Factor. It refers to the theoretical amount of time one can be in the sun without getting sunburn. The number that follows the SPF acronym indicates how much longer one can stay in the sun without getting sunburn.
If you normally start to get sunburn in 10 minutes, applying a sunscreen of SPF 30 would allow you to stay in the sun 30 times longer or a total of 300 minutes (10 minutes x 30 = 300 minutes or five hours).
However, SPF is a theoretical amount of time. If you are outside working, exercising, or just sweating, the actual amount of time the sunscreen will block the sun is much less. For this reason, it is recommended that sunscreen be applied every two hours.
Which SPF is best (15, 30, 50, or 100)? The American Academyof Dermatology recommends choosing a sunscreen with SPF of at least 30. The higher the SPF the more sunrays that are blocked and the longer you can stay in the sun. However, due to theoretical versus actual time discrepancy and the fact that higher SPF has more chemicals, some dermatologists recommend a SPF of 30 or 50 with liberal application every two hours.
The final sunscreen advice to keep in mind: No SPF sunscreen can replace the sun blocking ability of sun protecting clothing, umbrellas, or shelters.
The following website was used in answering the question:
http://www.onemedical.com/blog/live-well/spring-has-sprung-the-best-spf-protection-plan-for-rain-or-shine/