What Does the SPF of Sunscreen Really Mean?

So, what exactly does SPF in sunscreen mean?

We get this question often. Many people go to the store and choose the sunscreen with the highest SPF. It turns out this may not be the best way to choose sunscreen, let me explain….

First, I encourage you to read our articles in the “Healthy Skin” section of our website that talk about protecting the skin from sun exposure because I list the most important factors in choosing sunscreen. These factors include:

  1. Choose a non-oil based product
  2. Choose sunscreen with antioxidants built in
  3. Choose a sunscreen that thoroughly blocks both UVA and UVB radiation

When you choose a sunscreen by SPF alone, you may end up ignoring these other important factors.

So what is SPF?

The SPF number basically is a rating for the length of time that you can spend in the sun compared to if you wore no sun protection. For example an SPF of 25 means that you can hang out in the sun 25 times longer before you will begin to burn compared to if you wore no sunscreen at all. In fact, an SPF of 25 blocks 96% of the sun’s UVB radiation while an SPF of 50 blocks just 2% more for a total of 98%.

You can see how higher is not necessarily significantly better. In addition, the redness is caused by exposure to UVB radiation and thus the SPF only speaks to how well a sunscreen blocks the UVB radiation while ignoring the UVA radiation. It’s possible for a sunscreen to have a high SPF while offering little protection from the more lethal UVA radiation.

A good sunscreen should show protection from both UVA and UVB radiation and over recent years, the FDA has cracked down on how sunscreen manufacturers can label their sunscreens to make sure that UVA and UVB are both covered!

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