Experts Say a Higher SPF Isn't Always Better—Here's How to Choose the Right Level

Your SPF 100 armor isn’t as mighty as it seems.

In case everyone and your mother haven’t already told you, sunscreen is one of our most valuable resources for preserving skin and maintaining a (healthy) head-to-toe glow. “Proper sunscreen use is crucial for preventing sunburns, limiting hyperpigmentation, combating early signs of aging, and reducing chances of skin cancer,” says Erum Ilyas, MD, board-certified dermatologist and founder of AmberNoon.

But sunscreen isn’t always as straightforward as it seems. What counts as adequate application, and does a higher SPF always equate to a greater defense? If you use higher SPF, does that mean you can apply less sunscreen? We asked Dr. Ilyas everything you need to know about decoding that mysterious number on your sunscreen bottle.


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What does SPF mean?

If you find yourself confused by SPF (short for Sun Protection Factor), you’re certainly not alone. “One of the more common misconceptions surrounding SPF is that ratings tell us something about the time of sun exposure that could lead to a sunburn,” explains Dr. Ilyas. “The amount of UVB exposure varies based on the time of day you are outdoors, making it impossible for the SPF to provide a value that you could apply to the amount of time you can spend in the sun based on the time of day.”

Instead, Dr. Ilyas describes SPF as a value that’s assigned to a sunscreen product to inform the consumer of the sunscreen's ability to prevent sunburn when it’s used. “Sunburns are triggered by UVB light, and the SPF correlates to the amount (or percentage) of UVB blocked by the product.” You can think of the number as how long the UV would take to redden your skin versus the amount of time without any sunscreen. For example, it would take you 25 times longer to burn with SPF 25 than if you weren’t wearing sunscreen.

What does SPF level mean?

So, does a higher SPF level equate to greater defense? According to Dr. Ilyas, “it’s complicated.”

“When evaluating UVB charts, where SPF typically ranges from 93% (SPF 15) to 99% (SPF 100), it’s easy to see how SPF can get so confusing,” says Dr. Ilyas. “So many of my patients eager to protect their skin from skin cancer will tell me they only wear SPFs above 50. Although I tend to recommend an SPF of at least 30, I think it’s more important to consider how often you reapply the product instead of the number.”

She says this is because higher SPFs don’t necessarily offer significantly more protection. Contrary to what you may think, an SPF 100 wouldn’t give you double the protection of an SPF 50. In fact, both the EWG and the Skin Cancer Foundation agree that higher-SPF products are not that much better at shielding you from UVB—SPF 30 blocks nearly 97% of UVB radiation, SPF 50 blocks about 98%, and SPF 100 blocks about 99%. The FDA even went as far as to call sunscreens with SPF values greater than 50 "inherently misleading."

“Not to mention that higher SPF formulas are less cosmetically elegant to apply, making them more challenging to use routinely,” adds Dr. Ilyas. “Higher SPFs just tend to cost more, meaning well-intentioned consumers are spending more but not getting enough added protection to justify the cost.”

How Much Sunscreen to Apply

Of course, there’s also the matter of how much sunscreen we should actually be applying, and when. “One study suggests we should be applying 2mg/cm of sunscreen, whereas most apply only 20 to 50 percent of that amount (meaning the actual effectiveness of the sunscreen applied could likely be 20 to 50 percent lower than the SPF value listed),” Dr. Ilyas cautions.

She says the best way to address this discrepancy is to apply sunscreen generously and consistently, ideally every morning. “By making this a part of your daily routine, you’ll always have a base level of protection during the moments you didn’t expect to spend as much time outdoors or have inadvertent excess UV exposure,” she says. “If you are sweating or swimming, you may need to reapply your product every 40 or 80 minutes. Otherwise, plan on reapplication every 2 hours.” 

Dr. Ilyas reiterates the importance of this routine regardless of the season. “Many of my patients associated UV protection with heat, which explains why I tend to see the worst sunburns in March and April.”

Because of this, she suggests checking UV levels in real-time. “Open the weather app on your phone, scroll to the bottom right side of the screen, and look at the UV index at that moment,” she says. “A UV index of 0-2 is generally considered low-risk and 3-5 moderate, then you get into the higher-risk categories. This index changes based on the time of day and location so you’ll want to reassess it throughout the time you spend outdoors.” 

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