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Is There A Difference Between SPF & UPF?

by kelly / July, 11 2018 01:30

Photo of a day and his little girl walking on the beach on a sunny day

Let me get right to it – there is a difference between SPF and UPF. Many people confuse the two and it’s probably much better for your skin if you don’t Smile. But no worries we’ve got you covered and can easily explain the difference.

SPF Measures Sunscreen

SPF stands for Sun Protection Factor and is a measure of how long a sunscreen will protect you from UVB rays. What does that exactly mean? Well in theory it works like this – let’s say with no sunscreen your skin starts to get red in 20 minutes. An SPF 15 theoretically would allow you to stay in the sun 15 times longer without getting burned, for 5 hours while an SPF 30 theoretically would be double at 30 times and for 10 hours.

BUT and that’s a big BUT, it doesn’t account for your skin type, the amount of sunscreen applied and the intensity and wavelength distribution of UVB rays during the day and by location. The US Food & Drug Administration says its best to think of SPF “not directly related to time of solar exposure but to amount of solar exposure.”

So a better way to look at SPF is to think of it in terms of percentages: SPF 15 filters out approximately 93% of UVB rays, SPF 30 keeps out about 97% and SPF 50 about 98%. No sunscreen can block 100% of UVB rays but it’s important to wear sunscreen to prevent as much UVB exposure as possible.

Another important BUT on SPF is it doesn’t measure your protection against UVA rays. Generally UVA rays cause skin aging while UVB rays cause sunburn and both UVA and UVB rays cause skin cancer. I say generally because both rays damage skin and are thought to cause a bit of all the issues. To ensure your sunblock is also protecting you against UVA rays make sure you are choosing a product that offers “broad spectrum” protection. Those exact words need to be on the label of the product to ensure you are getting UVA protection.

Bottom line, I would NOT recommend being out in the sun with a broad spectrum SPF 15 for 5 hours. A great comment by the Skin Cancer Foundation:

“In the real world, no matter what the SPF, sunscreens start to lose effectiveness over time, so it’s important to reapply every two hours and after swimming or heavy sweating.”

UPF Measures Clothing

Now that you’ve got SPF down what does UPF mean? UPF stands for Ultraviolet Protection Factor and indicates what fraction of the sun’s UV rays can penetrate fabric. Thus a piece of clothing with a UPF 50 allows around 1/50th of the sun’s UV radiation to reach the skin.

UPF, unlike SPF, measures both UVA and UVB penetration.

The Bottom Line

To make it easier, here’s a little summary:


  • Only measures UVB protection (make sure the sunscreen is labeled “broad spectrum” to also get UVA protection)
  • Is the percentage of UVB rays filtered out
  • Applies to sunscreens


  • Measures UVB and UVA protection
  • Is the fraction of the sun’s UV rays that reach the skin
  • Applies to clothing

In the end, even though UPF and SPF are different both make up vital parts of any good sun protection regimen. So lather up on that sunblock and wear protective clothing when out in the sun.

Suncare Smarts

If you want to learn even more about SPF, broad spectrum protection and UV rays – check out the following posts:

Finally don’t forget our Suncare Smarts blog series for all your sun safety needs.

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