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Article: What is SPF? What Does The SPF Number on Sunscreen Mean

Brush On Block Mineral Powder Sunscreen SPF 30 with Brush On Block SPF 30 Mineral Sunscreen Lotion and a Portland Timbers ball cap.

What is SPF? What Does The SPF Number on Sunscreen Mean

Every dermatologist, general practice doctor and esthetician will tell you, you need to wear SPF 30 sun protection every single day. But this can lead to moisturizer has SPF 20, isn't that good enough? If SPF 30 is good, then SPF 75 is even better, right? If my moisturizer is SPF 20 and my sunscreen is SPF 30, I'm wearing SPF 50?  Wait, I thought it was SPF 15 for everyday? What does SPF 30 even mean? And what do all of those other things on my sunscreen mean? If I apply SPF 30 in the morning, I'm good for the rest of the day?

Settle in, we've got some answers for you!

What does SPF stand for?

SPF is short for Sun Protection Factor. In short, it is a ranking of the amount of UVB protection you receive when wearing that product. SPF does not measure UVA rays, more on that later.

What is SPF?

SPF measures how much UVB your skin can handle before burning. UVB rays are the rays that cause sunburn, and can also lead to skin cancer but SPF does not measure UVA, which causes photo-aging and can lead to skin cancer as well. To know that you are protected from UVA as well as UVB rays, look for the words Broad Spectrum on your sunscreen.

What does the SPF on your sunscreen mean?

Years ago, articles were written that explained the SPF number as a multiplier, the SPF number mean that you could be in the sun that many times longer before you would begin to burn. For example, if you would normally burn out in the sun in 5 minutes, you would multiply that times your sun protection factor, let's say SPF 30 in this case. 5 x 30 = 150, so in theory, you could be in the sun for 150 minutes wearing SPF 30 before you would begin to burn. But there are several problems with this math, and they are the reasons that you should only use this as the roughest possible guide to how long you are protected. 

The problems are:

1. It doesn't take into account your beginning skin tone. If you are very fair, you probably burn very quickly, and because no SPF protects 100% from the sun, your protection will not be effective for as long. 

2. It also doesn't take into account the intensity of the sun. If you are on a beach in Costa Rica, the sun is much more intense than if you are on the shore of a lake in northern Michigan. Seasons, time of day and how close you are to the equator all affect the intensity of the UV rays.

3. 150 minutes exceeds the amount of coverage you can count on from any sunscreen. If you read the Drug Facts panel of any sunscreen, it will tell you to reapply every 2 hours. This is not just a ploy to sell more sunscreen! If you are wearing a sunscreen with chemical active ingredients like oxybenzone or avobenzone, those really do lose effectiveness over time, and after 2 hours, your protection has lessened greatly. But even with mineral sunscreen, as you move around and touch things, your sunscreen can be wiped off. Every sunscreen should be reapplied after 2 hours in the sun, and even sooner if there is water or sweat involved. (More on that later.) So don't go thinking that since you burn after 30 minutes, and are wearing SPF 50, 30 x 50 = 1500 and 1500 divided by 60 minutes is 25 hours, so you're protected all day long and maybe into tomorrow! Not by a long shot. Use the "that many times longer before burning" math as a guideline, but no sunscreen can accurately predict the amount of time you can or should spend in the sun before you burn.

4. And as referred to in point #1, no sunscreen protects from 100% of UV rays. We'll go more into that, but suffice it to say, a lower SPF allows more of both UVA and UVB to reach the skin than a higher SPF, and Broad Spectrum is necessary to protect from UVA rays.

What Is SPF 30 Mineral Powder Sunscreen

Types of UV Rays

There are three types of UV rays, or UV radiation; UVA, UVB and UVC. The best way to remember them is that UVA = Aging, these penetrate deep into the skin and the damage shows up as aging (perhaps prematurely) skin. UVA damage can lead to melanoma and other types of skin cancer. UVB = Burning, these rays don't penetrate as deeply, and cause painful sunburn, and can also lead to skin cancer. UVC rays are the shortest, and are so short that they are filtered out by the earth's atmosphere and do not reach your skin.

What does Broad Spectrum mean?

Many people are surprised to learn that the SPF on your sunscreen refers only to protection from UVB rays, the rays that cause the skin to burn. And while that is very important, it leaves out the UVA rays, the ones that don't create a sunburn, but do contribute to skin aging. Both UVA and UVB rays can contribute to skin cancer. Knowing that this is important, the FDA established language for labels that shows that a particular sunscreen protects from UVA rays. If your sunscreen is not a broad spectrum sunscreen,  it almost certainly offers you no protection from UVA rays.  The words Broad Spectrum are your guarantee that you are also getting UVA protection from your sunscreen, and that it will help prevent skin damage in both the long and short term.

How does Sun Protection work?

This answer depends partly on the type of sunscreen you are wearing. If you are wearing a sunscreen with chemical actives (like avobenzone, oxybenzone, octinoxate, homosalate or several others), the sunscreen absorbs the sun's rays and converts them to heat through a chemical reaction, and then the heat is released from the skin. If your sunscreen is made with mineral actives (only titanium dioxide and zinc oxide), it does absorb some of the sun's rays, but reflects much of it off of the skin as well. Chemical sunscreen actives only absorb and do not reflect.

It is also important to remember that if you are layering sunscreen (maybe applying Brush On Block over an SPF 20 moisturizer) that the SPFs do not add up. 30+20 is 30, not 50.

How long does my sun protection last?

The simple answer is 2 hours. Every sunscreen, whether made with chemical actives or mineral actives, should be reapplied every 2 hours when outdoors. This gives you the best protection when you are dry, but if you are in water or sweating, you should also be aware of the water-resistance of your sunscreen.

How does sweat and water effect my protection?

If you are going to be in water, or sweating, you need to reapply your sunscreen more frequently than every 2 hours. How do you know how often? The label will tell you. Years ago, the FDA did away with the language "waterproof," and now no sunscreen is able to claim to be waterproof. Instead, there are three levels of water-resistant sunscreen. The first level is no water-resistance at all. This either means that the sunscreen washes off easily, or that the company decided not to have the product tested for water resistance. (This may often be the case with cosmetic items that include sunscreen. Since most people don't apply a foundation before swimming, the water resistance of that product is not important to most consumers.) If your sunscreen is not water resistant, it will not mention that on the front panel, and the Drug Facts panel will say something to the effect of "use a water resistant sunscreen if swimming or sweating." The next level is Water Resistant 40 minutes. This means that after being in the water (or in and out of the water, but air-drying) for 40 minutes, you need to reapply. And finally, there is Water Resistant 80 minutes. This is the highest level of water resistance, and means that if in and out of the water (or sweating) you need to reapply after 80 minutes of wear. But note, if you towel-dry any time you get our of the water, you have wiped off your sunscreen, regardless of which type you are using. All sunscreen should be reapplied immediately after towel-drying.

An interesting fact about Brush On Block® Mineral Powder Sunscreen is that it is Water Resistant 80 minutes. It seems counter-intuitive, how can a powder resist water? And yet it does, our mineral powder is hydrophobic, meaning it resists water. If you put some Brush On Block powder into a glass of water, you will find that you cannot mix it with the water. No matter how much you mix and stir, the powder comes back to the surface, and if you touch it, it remains dry. 

What does SPF 15 mean?

SPF 15 blocks 93% of UVB rays. Conversely, this means that SPF 15 allows 7% of UVB rays to reach your skin.

What does SPF 30 mean?

SPF 30 blocks 96.7% of UVB rays. This is commonly rounded up to 97%. So SPF 30 allows 3.3% of UVB rays to reach your skin, or about half as much as SPF 15.

What does SPF 50 mean?

SPF 50 blocks 98% of UVB rays, and allows 2% of UVB to reach your skin, or not quite half of what SPF 30 allows. Keep in mind that NO sunscreen blocks 100% of UV rays, and so the increase from SPF 50 gets smaller and smaller as the level of protection goes up. 

If SPF 30-50 is good, SPF 60-100 must be great, right?

Unfortunately, while they do offer slightly more sun protection than sunscreens in the SPF 30-50 range, high SPF sunscreens do not offer as much protection as you might think.Keeping in mind that SPF 50 blocks 98% of UVB rays, consider that SPF 100 blocks 99%. And then consider that this 1% increase in protection comes with a product that is probably thicker, goopier and if made with mineral actives, whiter on the skin than the SPF 30 or SPF 50 products you are used to. These higher spf values also create a false sense of security. If you use the old "that many times longer to burn" theory, even if you burn in 5 minutes, 100 times that long is 500 minutes or over 8 hours. But as we have already discussed, all sunscreens need to be reapplied every 2 hours, and this may seem silly if you think you are getting 8 hours of protection. No sunscreen can protect you for 8 hours.

How can I get longer-term protection?

Knowing that you should reapply every 2 hours (or sooner if you are sweating or in water), it makes sense to look for easy-to-apply sunscreens and other ways to avoid the UV rays, especially during the peak hours of 10 am to 2 pm. 

Brush On Block is your easiest solution for fast, on-the-go application. Simply brush the sunscreen onto your skin, and you have SPF 30 protection for the next 2 hours. (Remember though, to buff on a generous amount! People often make the mistake of not applying enough sunscreen, and that will give you much less protection.)

A good sun hat and protective clothing are also great ways to avoid excess UV exposure. Hats and clothing have UPF ratings, rather than SPF ratings, but they are very similar. UPF means Ultraviolet Protection Factor, and clothing with a UPF label protects not only from UVB but also from UVA rays. It should also be noted that repeated washing can remove the UPF from some clothing over time. Stretched or wet fabric also reduces its ability to protect.

Why is SPF important?

Everyone should protect their skin from UV rays every day. The health benefits of sun exposure are undeniable, the sun helps our body to create vitamin D, which effects our immune system, and protects our bones, muscles and hearts. But too much sun exposure has negative effects, most notably reddening of the skin, sunburn, photoaging (also referred to as sun damage) and increasing your risk of skin cancer. The best thing to do is to enjoy the sun but to wear a sunscreen every day to prevent the unwanted effects of UV rays. Dermatologists used to recommend SPF 15 for daily wear, but have now increased that to SPF 30, and specifically one that offers broad spectrum protection. 

FAQs SPF & Sunscreen

  • What does SPF stand for? Sun Protection Factor
  • What does the SPF number on sunscreen mean? According to, "the SPF number tells you how long the sun's UV radiation would take to redden your skin when using the product exactly as directed versus the amount of time without any sunscreen."
  • Is SPF 70 good? While any sunscreen is good because it protects your skin from UV exposure, SPF 70 only protects your skin from less than one percent more UVB rays than SPF 50 does.
  • What SPF is best for tanning? Wearing a sunscreen slows tanning as well as burning, so the higher the SPF, the longer it will take you to tan. This is a good thing though, as any change in skin color is an indication of skin damage. You may not notice the damage today, but in future years, you may regret tanning. The only truly safe tan is a fake tan.
  • Does SPF affect how long the sunscreen protects your skin? No. All sunscreens need to be reapplied every 2 hours, and sooner if you are in water or sweating.
  • What does SPF mean? Sun Protection Factor.
  • What is the difference between SPF 30 and SPF 50? 1.3%. SPF 30 blocks 96.7% of UVB rays, and SPF 50 blocks 98%.
  • What does SPF do to skin? Mineral sunscreen sits on the surface of the skin and absorbs some UV rays, and reflects others back into the atmosphere, protecting the skin from sun damage. Chemical sunscreen absorbs into the skin and a chemical reaction turns the light into heat, releasing that into the atmosphere and protecting your skin from damage.
  • What is a good SPF? Dermatologists recommend wearing SPF 30 every day.
  • What are some of the benefits of using an SPF? Sunscreen protects your skin from three things: Sunburn, Photo-aging and Skin Cancer. By wearing your sunscreen every day, you will have younger looking and healthier skin as you age.
  • What SPF do you use? Brush On Block Mineral Powder Sunscreen SPF 30 and Brush On Block Mineral Sunscreen Lotion SPF 30, of course.

Advice for Best Protection

If you want to keep your skin protected from the sun, but are going to be outdoors during peak hours, here is the best way to keep your skin safe:

Begin with a generous application of sunscreen everywhere that may be exposed. This is easiest to do before dressing, and that way if you have straps or shorts that may move with you, you won't have the reddening at the edges of exposed skin. Of course, for this, we recommend our new Mineral Sunscreen Lotion SPF 30. Then follow with UPF clothing. Next, apply Brush On Block Mineral Powder Sunscreen SPF 30 to your face, neck, arms, and hands. Did you already put the lotion on these areas? That's ok, extra coverage provides a safety net of coverage in case you. missed any spots or did not apply a large enough amount of sunscreen. (Generally, it takes one ounce of lotion to cover your entire body.) Then apply a hat and sunglasses, and lastly, a coating of our Protective Lip Oil SPF 32. You may think this looks odd, or that you're covering up too much, but believe us, ten years down the road you will be pleased with the way your skin looks! And remember, reapply as the day goes on, being sure that all exposed skin gets another coating of sunscreen.

What Is SPF Sunscreen Lotion