When choosing a sunscreen, you've likely reached for the one with the higher SPF number, but you might not know why. Many assume that a higher SPF correlates to increased sun protection, but what does SPF mean, exactly?

A lot goes into choosing a quality sunscreen, including the ingredients, amount of SPF, and so on. Understanding just how SPF impacts your sun protection can help make your decision a little easier.

What Does SPF Mean?

Firstly, SPF stands for "sun protection factor." The Food and Drug Administration defines this as a measure of how much ultraviolet (UV) radiation is required to produce sunburn on skin that's been protected with sunscreen. If you assume that higher SPF means more sun protection, you're correct. SPF 45 offers more protection than SPF 15.

The SPF number represents how long the sun's rays would take to sunburn your skin when the product is used as intended compared to the amount of time without sunscreen, according to the Skin Cancer Foundation. For example, after applying a product with SPF 35, your skin would take 35 times longer to redden than if you weren't wearing any sunscreen at all. Regardless, most sunscreens should be reapplied approximately every two hours for proper protection, per John Hopkins Medicine.

There are two types of UV rays—UVA and UVB—so it's important to note that SPF measurements only refer to protection against UVB rays. SPF numbers also indicate what percentage of UVB rays hit your skin. Still, this difference isn't as significant as you might think: SPF 15 blocks approximately 94 percent of UVB rays, and SPF 30 can block about 97 percent.

SPF: Fact or Fiction?

There are a lot of misconceptions about how SPF works. Here are some sunscreen facts to bust common SPF myths:

  • SPF doesn't relate to hours of solar exposure; it relates to the amount of solar exposure. SPF 15 doesn't mean you won't get burned for 15 hours. Instead, it means you're 15 times more protected than if you were in the sun unprotected.

  • People of all skin tones need to protect themselves with SPF products. If you're fair-skinned, you're likely to absorb more solar energy, but if you have darker skin, you're still at risk for sunburn, skin cancer, and other forms of sun-related skin damage.

  • Waterproof sunscreen doesn't exist. However, some water-resistant sunscreens can remain effective for a short period in wet conditions. Remember to reapply water-resistant sunscreen more frequently when swimming at the beach or sweating during exercise.

Choosing the Right Sunscreen

The American Academy of Dermatology recommends an SPF of at least 30. This offers adequate sun protection and has greater staying power. The EltaMD UV Daily Broad-Spectrum SPF 40 is a great choice for everyday sun protection.

Seeing as SPF only defends against UVB protection, always opt for a broad-spectrum sunscreen to ensure protection against both UVA and UVB rays. If you'll be exposed to wet conditions, remember to grab a water-resistant sunscreen. The EltaMD UV Sport Broad-Spectrum SPF 50+ is water-resistant for up to 80 minutes, so be sure to reapply as directed for maximum protection.

Now that you know what SPF means and how it works, you can apply your sunscreen every day with the confidence that you're doing what's best for your skin.

Which EltaMD Sunscreen is right for you? Chat with Elyse to find your ideal match, or read up on EltaMD's sun protection options.


  • Lacey Muinos

    Lacey is a Southern California-based freelance writer who combines her passions—fitness, health, and a vegan lifestyle—with her work to help readers feel and be their best. Her work has been featured in Healthline, Livestrong, Verywell Fit, Eat This Not That, KinderBeauty, and more.

    View all posts