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Here’s What Those SPF Numbers Mean

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Here’s What Those SPF Numbers Mean

What do SPF numbers mean? When it comes to SPF 15 vs. SPF 100, there’s a big difference! Here, we break it all down for you – and tell you why the only ones you should focus on are between 30 and 50.


Many of us have a pretty general understanding of what SPF numbers mean. For example, common sense tells you that SPF 15 is going to provide less protection from the sun than SPF 30. But what exactly do these numbers indicate?

With the help of Chris G. Adigun, MD, a board-certified dermatologist in Chapel Hill, we’re going to do a deep dive into the world of SPF to learn about where those numbers come from and how they’re configured before being slapped onto a label. We’re also going to address why you should always use SPF 30 to 50 and why a super high SPF can be a bad thing.

What does an SPF number measure?

First of all, here’s a fun fact you might not be aware of: your skin actually has a built-in defense mechanism against UV rays. Unfortunately, this protection (which is basically just natural oil secretion) isn’t what you’d describe as adequate. In fact, depending on your skin type, you can only be in the sun for five to twenty minutes before damage starts to occur. Repeated damage can lead to expedited cell break down, which can cause all those signs of aging that we’ve talked about before—fine lines, wrinkles, tightness and hyperpigmentation—and, worst of all, skin cancer.

This is why extra protection is so important, which brings us to SPF. SPF stands for “sun protection factor,” and it’s a measure of protection from the sun’s UVB rays. The corresponding number is a measurement of how long your skin will be protected (read: sunburn-free) from these rays when you use the product correctly, versus the amount of time it would take without using it at all. And while it’s true that darker skin tones produce more melanin, which gives them a “built-in SPF” in their skin, that SPF number is low, so low that it won’t protect your skin from getting burned or being affected by the aging effects of UVA rays.

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The only way to know if a sunscreen provides both UVB and UVA protection is if it actually specifies “broad spectrum” on the label.

“That means that if a sunscreen has an SPF rating of 15 or 30, it will take 15 or 30 times longer to redden the skin when it is covered with that product,” says Dr. Adigun. She adds, “And I can’t emphasize enough that this rating is only a measure of protection from UVB rays and not UVA ones.”

As a side note, the only way to know if a sunscreen provides both UVB and UVA protection is if it actually specifies “broad spectrum” on the label. “UVA rays penetrate the skin more deeply and are thought to be the key players in the development of skin cancer and premature aging,” says Dr. Adigun. “Therefore, products with broad spectrum protection will decrease the wearer’s risk of developing melanoma and non-melanoma skin cancers due to sun exposure.”

Every Supergoop! sunscreen boasts broad spectrum protection, and you won’t find one under SPF 30, either.

OK, so what SPF numbers do I need to be on the lookout for?

All skincare experts—including the best dermatologists in the world—recommend wearing an SPF of 30 or higher for daily protection. Anything less really isn’t enough. Experts will also tell you that an SPF between 30 and 50 is completely sufficient, and that there’s really no reason to reach for stratospheric numbers like 70, 90 or 100. Here’s the breakdown of the most popular SPF numbers out there and the exact percentages of the sun’s rays that they protect you from:

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“The index of protection going from SPF 0 to SPF 30 is enormous, whereas the measure of benefit above SPF 50 is less significant,” explains Adigun. She also explains that the biggest downfall of high SPF is that it gives wearers a false sense of all-day protection, and they’re less likely to reapply every two hours (resulting in more cases of sunburned skin). Furthermore, any SPF over 50 will also expose the skin to a much higher concentration of active ingredients than necessary.

Does formulation and texture change as SPF gets higher?

The answer to this question isn’t always clear cut.

“[Sometimes], chemical sunscreens with water-resistant components can be oily in an effort to resist washing off easily with water or sweat exposure. In contrast, mineral-based sunscreens—which are made with zinc oxide and titanium dioxide—can be thick and leave an opaque white cast on the skin that is cosmetically displeasing,” says Dr. Adigun. “However, there are many water-resistant sunscreens available that are not oily, and many mineral-based sunscreens that are completely translucent.”


Our formulas are prime examples. Our Smooth and Poreless 100% Mineral Matte Screen is a mineral-based sunscreen with SPF 40. It’s not chalky at all, and in fact can be used as light coverage or as a makeup primer under your favorite foundation with zero risk of a white caste. And our Glow Stick Sunscreen, which is an oil-based chemical sunscreen with SPF 50, sinks beautifully into skin for that lit-from-within goddess glow without any of the greasy nonsense to worry about.

Bottom line:

“What I recommend to my patients is to find a sunscreen that is broad spectrum with an SPF of 30 to 50 with a texture, feel, and fragrance that they like,” says Adigun. “I’ve found that if my patients like it, then they’ll wear it!” So, in other words, pick any Supergoop! sunscreen and know that it will include the right amount of SPF to fully protect you.


+What SPF number do you tend to gravitate towards? Share your pick in the comments!

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