What is SPF?

Have you ever found yourself staring at a drugstore shelf wondering, “What’s the actual difference between SPF 30 and SPF 75?” or “what is SPF anyways?” you’re not alone.  

We’ve heard some choose a lower SPF because they want to get a better tan. Some think SPF 100 protects against more sun damage than SPF 50. But neither case is necessarily true. 

We often trust what we read on labels, without considering how a product earns the right to make a sunscreen claim. 

So let’s explore what SPF is and what an SPF rating really means. 

The Basics—What is SPF? 

SPF stands for Sun Protection Factor, or “the level of sunburn protection provided by the sunscreen product.”  

In order to make an SPF claim, all sunscreen companies must go through the Foods & Drug Administration’s standard exposure test. The SPF test measures the amount of ultraviolet, or UV, exposure it takes to cause a sunburn while a person is wearing a certain sunscreen, compared to the amount of UV radiation it takes to burn while a person is wearing no sunscreen at all.   

The product is then labeled with the appropriate SPF number—the higher the number, the greater level of sunburn protection.  

But this test isn’t comprehensive. 

The government’s SPF test only measures protection from UVB radiation, or “burning rays.” While frequent sunburn is a known cause of skin cancer, it’s only one harmful effect from only one type of UV ray. 

Harmful sun exposure reaches the surface of the earth in two forms 

  • UVA rays cause aging, like wrinkles and age spots.  
  • UVB rays cause sunburn.  

UVB rays are the more intense, and tend to cause the most damage to the outer layer of the skin. However, UVA accounts for about 95% of radiation that reaches the surface of the earth, maintains consistent intensity throughout the day, and has the ability to penetrate clouds and window glass.  

Protect yourself from a range of sun damage by selecting not only the correct SPF but also a sunscreen with “broad-spectrum” protection 

It’s a designation only available to sunscreens achieving SPF 30 or above. But how do you know you’re using the right SPF?  

Does a Higher SPF Really Mean More Protection?  

It’s true that SPF is the “theoretical amount of time you can stay in the sun without getting sunburned,” but it’s a common misconception that higher SPF means you’re preventing more damage. 

“SPF is not a consumer-friendly number,” dermatologist James Spencer told WedMD.  

“It is logical for someone to think that an SPF of 30 is twice as good as an SPF of 15 and so on. But that is not how it works.” 

For the average person, it takes about 10-20 minutes for unprotected skin to start burning. Logically, this should mean that applying an SPF 15 would allow you to stay in the sun 15 times longer, or up to 5 hours. But this thinking doesn’t consider sweating, swimming, or rubbing off on clothing or towels. 

In reality, it’s unlikely that one sunscreen application would remain fully effective for more than 2 hours.

In actuality, there is very little statistical difference between SPF 50, and SPF 100.

SPF 15 Blocks approximately 93% of UVB rays
SPF 30
Blocks approximately 97% of UVB rays
SPF 50
Blocks approximately 98% of UVB rays
SPF 100
Blocks approximately 99% of UVB rays


Even though the difference between SPF 50 and SPF 100 is over 50 points, the percentage of UV protection only increases 1%. After you reach SPF 50, there’s no need to go any higher, says Dr. Spencer. 

If you’re applying your sunscreen correctly, any SPF between 30 and 50 will provide sufficient protection, even for those with the most sensitive skin.

For your face and body, we suggest choosing an SPF 50, because it leaves more room for human error. In order to get the full benefit of the labeled SPF value, we should be using about 2 milligrams of sunscreen per square centimeter of skin, but in reality, most of us only use about a quarter of that amount.

Since most of us have a hard time envisioning 2 milligrams/square inch, we suggest about a dime-sized amount for your face, and about a nickel or quarter-sized amount for each limb and your torso.

Choosing the highest known-effective SPF value is a good rule of thumb to give everyone a healthy safety margin. 50 is always a reliable choice, and the highest proven effective SPF rating approved by the FDA and American Academy of Dermatology.

Products Over SPF 50 May Do More Harm than Good

It’s always important to remember that no sunscreen can block 100% of the sun’s rays.

Protection over SPF 50 becomes more and more gradual, and in fact, you may actually experience a point of diminishing returns.

A product over SPF 50 may pass the broad-spectrum test, but there is no consensus on how much UVA protection a “broad-spectrum” sunscreen provides. While UVB-heavy coverage won’t cause a sunburn, the lack of UVA coverage could still be harmful to your health and the aging process.

It could also create a false sense of security, lulling people to forgo protective clothing and perhaps stay out in the sun longer. These are some of the reasons Australian and European governments have established guidelines for UVA testing and capped SPF labels at no more than 50.

Although the FDA has commented that SPF labels are “inherently misleading” (FDA 2007), they have yet to enact any regulation.

There is no safe way to tan 

Spending time outdoors in the sunshine contributes to our levels of Vitamin D, not to mention our overall happiness. But it’s important to keep in mind that overexposure to any type of UV radiation undeniably causes cancer, according to the U.S. Department of Health & Human Services and the World Health Organization’s International Agency of Research on Cancer.

The American Academy of Dermatology is quick to remind us that “there is no safe way to tan.” Each time you tan, you contribute to skin damage, and damage compiled over time increases your chance of melanoma.

How Can I Be Sure I’m Safely Protected?

A sky-high SPF label typically indicates a highly chemical formulation. This is because companies need to add significantly larger concentrations of sun-filtering chemicals in order to reach the higher SPF threshold. According to the EWG, the jury is out on whether many sunscreen ingredients are “safe” as deemed by the FDA.

To be sure you’re getting the coverage you need, opt for a “physical,” or mineral sunscreen.

Mineral sunscreen acts as a shield against the sun’s rays.

Think of physical sunscreens as reflectors.

With the power of minerals like Zinc Oxide and Titanium Dioxide, physical sunscreens are not absorbed, but sit on top of the epidermis. When it comes into contact with sunlight, these sunscreens bounce UV rays off of the skin’s surface, thereby preventing radiation from ever entering the body.

Compare this method to products with chemical ingredients, which are known to absorb ultraviolet radiation into the skin, and by changing the electromagnetic radiation effect, expel the UV as infrared rays.  

If that sounds complicated, that’s because it is complicated. To keep your routine natural and streamlined, choose mineral sunscreen to keep your skin as safe as possible.

Making The Choice 

Next time you find yourself in the drugstore aisle, we hope you’ll reach for broad-spectrum, physical SPF 50 with certainty that you’re making the right decision.

To get the most well-balanced sun protection, skip the drugstore aisle entirely and shop Sunology online. Using broad-spectrum, physical protection, Sunology is the best mineral sunscreen with zinc oxide and titanium dioxide to shield your skin from UVA and UVB rays, while keeping your body healthy.

Have a question about Sunology, SPF, or mineral sunscreen? Don’t hesitate to reach out to us! We’re always happy to help. Contact Us

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