What do the different SPF numbers mean on sunscreen?

Last Updated: June 18, 2021

Wondering which sunscreen SPF number is right for you? Follow along for expert advice on the meanings of different SPF numbers!

It’s summertime, and with it comes all those fun, summertime outdoor activities you don’t want to miss. It also means a need for a good natural, mineral, or zinc oxide sunscreen.

However, choosing a good SPF suncare routine requires a bit of foreknowledge about what SPF actually is and what those numbers mean. We’re diving in so get ready!

Mrs. Meyers cleaning products and Grove Co. cleaning caddy

Become a Grove member

Wondering who Grove is, what types of products we offer, and how to get a free gift set when you sign up? Learn more about flexible monthly shipments, customizing your shipment, and joining millions of happy households — no monthly fees or commitments required.

What’s SPF exactly?

Yellow sun illustration

SPF, short for “Sun Protection Factor,” tells you how efficiently a sunblock or sunscreen protects your skin from UVB rays. UVB rays are known to cause damage to the skin, ranging from a simple case of sunburn to severe conditions such as skin cancer.

According to skin expert Steven Q. Wang, the SPF number of your sunscreen informs you on how much time you’ve got before your skin might react to the sun’s rays. Reactions include mild reddening to actual sunburn. For example, by applying a sunscreen with an SPF 30 to your skin, that means it’ll take 30 times longer to burn than if you didn’t wear any sunscreen whatsoever.

However, the label SPF of a sunscreen product can’t determine the exposure time of your skin to the sun. That actually depends on your skin type, the amount of sunscreen you’ve applied, as well as the intensity of the sunlight, and your sunscreen’s SPF rating. These factors are explained in more detail down below.

How do different skin types react to sun exposure?

Different skin types can differ in the severity of their reactions to sun exposure. Through the process of evolution, people from certain areas sometimes show minor differences in their appearance. Those differences appear to play a role in helping them adapt to their environment.

For instance, people that live in cold climates, with fewer sunny days and cloudier skies often have lighter skin that appears quite pale. Whereas people living in areas of high sun exposure often develop a larger amount of melanin, which results in darker skin tones.

People with the fairest skin tones tend to be the most vulnerable to sun damage. That means they are more prone to sunburn and have a higher risk of developing skin cancer. People with darker skin tones typically have a lower risk of skin cancer and sunburn, since they aren’t as skin sensitive to sunlight. However, people of all skin tones should still apply SPF to avoid any damage from UVB and UVA rays to the skin in general.

How much sunscreen should you use?

Image of mother putting sunscreen into child's hand while sitting outside on picnic blanket

You might not know it, but the amount of sunscreen you apply is actually a big contributing factor to how much time you can safely spend exposed to the sun.

According to board-certified dermatologist Elizabeth K. Hale, as a general rule of thumb, you should use about 2 milligrams of sunscreen per centimeter square of your skin in order to be adequately covered and protected. So what does that mean, exactly?

As an average-sized adult, you need about 1 ounce –– roughly 2 tablespoons –– of sunscreen to cover the exposed areas of your face and body, with almost one-third of it going to your face.

Sunscreen also needs to be reapplied every 2 hours for proper coverage and always applied at least 15 minutes before sun exposure. There’s usually a 30 minute time frame before water exposure for waterproof sunscreen as well.

Most people apply much less sunscreen than what’s actually needed, often using as low as one-fourth of the required amount. This leads them to question the efficacy of the sunscreen product after noticing sunburn or tanning. However, it’s not your product that’s the problem, it’s your application method. You need more than you think!

Do you need sunscreen on cloudy days?

Even when it’s cloudy skies for as far as the eye can see, the sun is still there, and the sun's rays are penetrating through the ozone layer. That means you should still be slathering on a high SPF sunscreen within your skincare routine! Just because it’s cloudy and the sun doesn’t feel hot, doesn’t mean you aren’t taking a hit.

Same goes for areas with snow-covered terrain. You might think you don’t need sunscreen while it’s snowing but you would be wrong. Snow is excellent at reflecting the rays of the sun, throwing them directly on your body.

Additionally, where the sun is located during its daily cycle also contributes to the intensity of those rays. For instance, morning sun is less intense than noontime sun, and evening sun is less intense than noon or afternoon sun. Typically after 3pm the heat starts to wane somewhat, and the sun’s rays aren’t as strong.

Back to SPF: What do the different SPF numbers actually mean?

Once you understand the different factors that impact your sun exposure and your risks, you can determine the SPF rating you need for your skin. The lowest SPF rating available is 15, which provides some protection, but not much.

You should use a product with a minimum of SPF 30 to provide proper protection, especially if you’re fair-skinned or have skin that’s sensitive. Keep in mind that where you are in the world can have an effect on what SPF you should choose as well.

For instance, the minimum recommended SPF and the amount you need to apply may different in a country like Australia, which is a very hot place.

Here’s a breakdown of the most common SPF numbers:

SPF 15

SPF 15 is the most basic level of sunlight protection. However, it still provides you with 93% protection from UVB rays.

In other words, if 100 photons of light were to penetrate the skin when there was no layer of sunscreen, a layer of SPF 15 sunscreen would block about 93 of those photons and only allow 7 of them pass through.

SPF 30

Following the same example, a layer of SPF 30 on your skin blocks 97% of light photons, and only allows 3 of them to penetrate into your skin. So, an SPF 30 sunscreen blocks 97% of UVB rays.

However, you might notice that there is not a huge difference between the protection SPF 15 and SPF 30 sunscreen offers. Though SPF 30 should offer double the protection, SPF 30 actually only gives 4% more protection than the SPF 15 product. Yeah, kind of breaks our brain too!

SPF 50

Similarly, as in the case of SPF 50, it only allows in about 2% of photons. So that means it blocks about 98% of them and provides only 1% more protection from the UVB rays than SPF 30.

SPF 100

The EWG and the FDA both agree that SPFs above 60 are misleading and not really any better at protecting you from sunburn or other sun ray symptoms and issues. When it comes to SPF 100, you’re really only getting 1 more percentage of protection from SPF 50. It goes up to 99%, letting 1% of photons in.

So isn’t 99% better? Not necessarily. In most cases, this comes with a lot of chemicals to get an SPF that high, so in order to get that one extra percentage of protection you’re actually exposing your skin and body to more chemicals that may cause other harm. Plus, people tend to stay out in the sun longer due to a false confidence with higher SPF sunscreen numbers, leading to sun damage and, in some cases, melanoma.

Blue bottle illustration

What is broad spectrum?

In nature, there are two types of Ultra Violet (UV) light rays coming from the sun that can cause potential damage to the skin. Where UVB rays cause more traditional and instantaneous symptoms and reactions –– like sunburn –– UVA rays are the baddies that cause wrinkles, premature aging, as well as sun and age spots.

Sunscreen products with a “broad spectrum” label on them are the best to use if you want to fully shield your skin from the broad spectrum of UV rays. Generally, broad spectrum sunscreen products should have at least one-third of the amount of SPF protection for UVA rays as it does UVB rays.

Unfortunately, this is an area where certain brands can be misleading. They may display the higher SPF rating for the UVB rays on the label, but, meanwhile, the UVA rays are wreaking havoc on your skin due to subpar protection.

As you can see, just because a sunscreen label has a high SPF rating, that doesn’t automatically mean more coverage or protection, at least not by a significant amount. However, it’s still a commonly held belief that the higher the SPF rating, the more you will be protected. While that might be somewhat true, it’s really not the full picture.

So how can you fully protect yourself from the sun?

You can’t really, short of avoiding the sun altogether. Since that’s not realistic, you can do the next best things. Wear at least a 30 SPF sunscreen, make sure it’s a broad-spectrum formula, reapply every 2 hours, and time your outings so that you aren’t out during the hottest part of the day. Typically early mornings and late evenings are the coolest times when the sun isn’t quite as intense. Read through our natural sunscreen guide to ensure your sunscreen is also chemical free for that extra protection.

You can also wear protective clothing that helps shield your skin from the sun, and invest in a great hat collection to keep the sun off your face. Just make sure any sun hats you wear have a dark rim to help absorb some of the sun’s rays that reflect off water. You might even consider carrying a small umbrella to provide extra shade in a pinch!

You don’t want to limit your time in the sun completely, because sunshine makes the heart shine (and gives you some much needed vitamin D! Just be safe about it and do all you can to keep your skin protected. Plus, we here at Grove are always gathering more information on some of the best natural sunscreen brands today!

Read more from Grove