What does SPF really mean?

Brittany asks…Ok, I feel kind of stupid asking this because everyone else probably already know this but what exactly does SPF mean? I mean I know it stands for Sun (Solar?) Protecting Factor but what does that mean?

The Right Brain responds:

As far as we’re concerned, Brittany, there are no stupid questions. In fact, you raise a very good question because we think that a lot of people are unclear of the real answer. So, in today’s post we’ll spell out exactly what SPF means.

The ABCs of SPF

First of all, you were close on the meaning of the acronym. SPF actually stands for Sun Protection Factor. This factor is a measure of how much Ultraviolet, or UV, radiation it takes to burn your skin when it’s unprotected compared to how much it takes to burn it when it’s slathered in sunscreen. The higher the SPF value of your sunscreen, the more protection it offers from sunburn.

Now, here’s the tricky part. Many people think that SPF relates to how much time you can spend in the sun. In other words, if you can stay in the sun for 30 minutes before burning and you wear a sunscreen with an SPF of 10, you should be able to stay in the sun for 30 x 10 = 300 minutes or 5 hours before burning. Right? WRONG!

Why is it wrong? Because SPF doesn’t just relate to the duration of sun exposure – it relates to the amount of sun exposure. Time is one factor that contributes to the total exposure level but it’s not the ONLY factor. The intensity of the UV radiation also impacts the amount. For example, one hour of sunlight at 9:00 in the morning is equivalent to 15 minutes of sunlight at 1:00 in the afternoon. So if you’re only looking at how long you’re out in the sun you might drastically under estimate how much sun exposure you’re really getting. Geography is another factor: sunlight is more intense the closer you are to the equator. And weather is yet another consideration: even though you can get a sunburn on cloudy days, the effect of sunlight is generally more intense when the sky is clear.

The Beauty Brains bottom line

The SPF value of a product does NOT tell you how long you can stay out in the sun before you burn. It only tells you the relative difference between the level of protection provided by different products.

Source: FDA.gov

Do YOU have a favorite sunscreen? Leave a comment and share your thoughts with Brittany and the rest of the Beauty Brains community.