What’s SPF in Sunscreen? SPF Level Breakdown

Sunscreen comes in all shapes, sizes, and most importantly, SPF values. When you go shopping for sun protection, you'll likely face a wall of countless SPF numbers emblazoned across colorful bottles, ranging in SPF value from as low as 2 (those with fair skin, beware) to as high as 110. But before you side with a specific brand or a type of sunscreen, you should know what is SPF?

We're going to give you an SPF level breakdown on what SPF in sunscreen is and how it works to help take the guesswork out of your UV protection. (Bonus: knowing what SPF is can make for some impressive poolside conversation.)

What's with all the acronyms?

Science usually has ways of consolidating really long words into things like SPF, UVA, UVB - but don't let these words intimidate you. Let's start here: What does SPF stand for? SPF stands for sun protection factor, and is a relative measurement of how long you are protected from UVB rays. You're probably thinking, "OK, so how about those UVB rays?" We'll get into that next, but let's go in alphabetical order. It's important to remember that the sun is a powerful thing, and its light is made up of different types of rays: UVA and UVB. According to the University of Iowa Hospitals and Clinics, these rays are both forms of ultraviolet light that play a role in the damaging of skin, from sunburn to skin cancer formation.

UVA rays affect your skin differently than UVB rays and attribute to things like premature skin aging, also known as wrinkles. UVB rays, on the other hand, cause sunburn and play a crucial role in the cause of skin cancer according to the Skin Cancer Foundation.

How does SPF work?

Now that we've gotten the acronyms out of the way, let's hone in on how SPF works. First, you should know that SPF is measured by its effectiveness in blocking the sun's UVB rays, not UVA rays. Remember, UVB rays are responsible for sunburn, which is exactly how SPF gets its number. Let's break it down.

The SPF value represents the factor in which you are likely to burn. In an example used by Skin Cancer Foundation, the SPF number is a multiplier of how long it takes your skin to burn without the use of sunblock. So that means if it takes your skin 10 minutes to burn without the use of sunscreen, then wearing a sunscreen with SPF 30 will take you 30 times as long to burn, assuming you applied it properly (always follow the directions provided by the sunscreen company).

More detail on broad spectrum protection

Getting back to those UVA rays. You may be wondering how the SPF number plays into the protection from UVA rays. That's where broad-spectrum sunscreen comes in. Ensuring you have broad-spectrum sunscreen with a minimum SPF of 15 will mean you're protected from the sun's harmful UVA and UVB rays. Although, that wasn't always the case. According to Skin Cancer Foundation, the FDA "issued new rules for sunscreen labeling," which meant companies had a standard to meet when labeling their products "broad spectrum."

Luckily for tax-free users, eligible sunscreen must carry a minimum of SPF 15 with broad spectrum protection, so the convenience of finding the most-protective UV protection is built directly into tax-free spending.

How does SPF block the rays?

That's the thing, it doesn't. SPF is just the indication of how much protection you will get from that sunblock. (We just went over this.) What does block the rays are the actual active ingredients used in the sunscreen. This is commonly divided into two categories: chemical or mineral. The common active ingredients used in chemical sunscreens (avobenzone or oxybenzone) actually absorb the Uv radiation, break it down, and release it as heat, as described by Live Science.

In comparison, mineral sunscreens which commonly use ingredients like zinc oxide and titanium oxide, are (as their name implies) physical minerals that sit atop your skin and physically reflect the UV rays. Sure, it doesn't sound nearly as scientific, but it is effective and a great alternative for those who have sensitive skin and are interested in more environmentally conscious options. Find which sunscreen is right for you and stick with which protects you best.

Does a higher SPF block more rays?

Technically, yes. Sunscreens do their best to block as many UVB rays as possible, but no sunscreen blocks 100 percent of all UVB rays. As determined by ConsumerReports.org, sunscreens with high SPF values of 100 and more, may not be more protective than an SPF 30 or SPF 50, which already blocks 97-98 percent. There's also the risk of entrusting higher SPF values to protect you for longer than lower SPF numbers, which can put you and your loved ones at risk of UV damage.

The sun doesn't deserve all this bad rap though. While its UV rays can be harmful, moderate amounts of exposure to sunlight is beneficial to your health. You may have heard that sun exposure is important for the production of vitamin D, which is true! According to the Skin Cancer Foundation, it only takes about 10-15 minutes of exposure to the sun on the arms, legs, abdomen, and back, two to three times a week to benefit from the sun's rays. The Foundation also explains that UVB rays are responsible for "triggering vitamin D production in the skin." While SPF indicates the protection from UVB rays, there's no proof that shows higher SPFs can diminish your body's ability to maintain vitamin D sufficiency.


From SPF to UVA and UVB, the most important takeaways you should have on your next sunscreen purchase should include: broad spectrum, a minimum SPF 15 value, and most importantly, follow the directions! Don't be fooled by high SPF numbers and always remember to reapply your sunscreen throughout the day! Now take what you've learned about SPF and impress a friend or two next time you're poolside.

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