What Does the SPF Number Mean?

Any skin care advice that does not include applying sunscreen every day, is not advice you should trust. Study after study has found that sunscreen is a critical element in protecting against sunburns, skin cancer, discoloration, and signs of aging like wrinkles and sagging skin. Even if you're inside or in a cloudy climate, the sun’s UV rays are at work, damaging your delicate skin. So turning to the sunscreen options in the skin care aisle or online is the first, most important step for healthy skin. 

But with so many different options with all kinds of different labeling, choosing the best one can feel daunting. If you are one of our fair skin friends, or just extra cautious when it comes to skin care, you may turn to high SPF options reaching up to SPF 75, 80, and even 100, but how much difference are they really making in protecting your skin?

What does SPF mean?

SPF stands for Sun Protection Factor, and there are a couple of elements that affect this number. In short, it is a measure of how much the sunscreen will protect against UVB rays.

So what exactly do the numbers mean? According to WebMD, the numbered SPF rating is “a measure of the time it would take you to sunburn if you were not wearing sunscreen as opposed to the time it would take with sunscreen on”. No, that doesn’t mean an SPF 15 sunscreen will only allow 15 minutes of sun protection.

The math breaks down like this: the amount of time it takes your skin to burn in the sun without sunscreen x the SPF = the number of minutes you can spend in the sun without getting burned if the sunscreen is adequately applied (more on that later).

This is a lot of info to take in especially if math isn't your forte, so let’s put it into a scenario to make it a little simpler. If your skin starts to redden after ten minutes without sunscreen, then while using an SPF 15 sunscreen it will take 150 minutes to burn.

Percentage wise, SPF 15 let's 1/15 of UVB rays hit your skin, so the product blocks about 93% of UVB rays; an SPF 30 let's 1/30 of UVB rays hit your skin, so the product blocks 97% of UVB rays; and an SPF 45 let's 1/45 of UVB rays hit your skin, so the product blocks about 98% of rays. SPF 100 lets 1/100 of UVB rays hit your skin, so it gives up to 99% protection. 

Confused? Don't be. All you need to know is that the difference in protection between SPF 15 and SPF 100 really isn't all that life changing.

percent protection from UVB rays by SPF

 

The importance of applying the correct amount of sunscreen

The SPF number is only accurate if you're applying the right amount of sunscreen. Most people are not using enough sunscreen, and using less sunscreen than necessary cuts the effects of the SPF value.

How much sunscreen should you use? You should use about 2 milliliters of sunscreen for every square inch of skin, which equates to about 2 tablespoons/1 ounce (about a shot glass size amount) for the whole body and face (a nickel size amount for the face alone).

Is higher SPF better?

No sunscreen can completely block out the sun, so shelling out your money for the highest SPF choice isn't 100% necessary, and there's more to sunscreen than just it's SPF.

As you can see in the graph above, there isn’t a huge difference between lower SPFs and higher ones as far as the percentage of protection from UV rays, and seeing as all sunscreen needs to be reapplied every two hours as it starts to fade, there’s really not all that much benefit of a high SPF.

Higher SPFs do have a higher protection percentage, but that can easily mislead you into spending too much time in the sun, neglecting to reapply, or not using other protective measures like time in the shade, sun hats, or protective clothing. SPF 100 offers slightly more protection, but it is not the superhero that clever marketing campaigns make it out to be. 

Higher SPF also tends to come with more ingredients that can cause irritation or other harm.

The American Academy of Dermatology, The Skin Cancer Foundation, The FDA, World Health Organization and the CDC all recommend SPF 15 or higher, and to reapply every two hours. The experts aren't recommending a super high SPF, so don't let skin care brands' marketing trick you into thinking otherwise.

Does SPF protect against UVA rays too?

As aforementioned, there’s more to sunscreen than just SPF.

A lack of education leads many people to just choose the highest SPF thinking it’s the safest option, but it only provides information on the UVB protection, and does not give any indicator of protection against UVA rays.

UVB rays drop off in cloudy weather which is why a winter sunburn is rare, but UVA rays are still at work damaging the deeper levels of skin. The earth's ozone layer absorbs most UVB rays, but studies show that somewhere between 90 and 99 percent of the ultraviolet light that reaches people is UVA radiation (Johnson 1976, Seckmeyer 2008).

There is no rating system for UVA rays in America, so a lot of time’s people are unprotected from the aging and skin cancer causing effects of overexposure to UVA rays.

If you want what’s best for your skin, choose a sunscreen that is “broad spectrum” which means it will provide protection from both UVA and UVB rays. These sunscreens contain mineral ingredients like zinc oxide and titanium dioxide which not only provide UVA and UVB protection, but are also a safer option than sunscreens that use chemical ingredients like oxybenzone and octinoxate. 

When your ready to restock your sunscreen, choose a sunscreen with at least SPF 15 (SPF 30 is a good middle ground), but also lookout for one labeled mineral and broad spectrum.

Cleure's SPF 30, broad spectrum, mineral sunscreen will set up your skin to fight sunburns, skin cancer, discoloration, and aging.

UVA vs UVB Protection

broad spectrum sunscreen protection vs spf

More Sunscreen Tips

Now you know a little more about SPF, check out these other Cleure Advice by Concern Blogs for more sun protection information and tips.

Choosing Sunscreen for Sensitive Skin

Why Sunscreen is Your Best Friend for Anti-Aging

Complete Guide to Sunscreen and Sunburn Protection

Guide to Reef Safe Sunscreen

Why You Should be wearing Sunscreen Indoors