SPF, which stands for “sun protection factor,” is a measurement of how well a sunscreen product protects your skin against UVB rays—the type of UV rays that can cause sunburns. More specifically, the SPF number tells you how long it would take for your skin to redden while wearing a specific sunscreen product versus not wearing any sunscreen at all. For example, your skin would theoretically take 50 times longer to redden with an SPF 50 sunscreen than it would without one (when measured under the same circumstances).
Sunscreens are formulated with a range of SPF values, with some of the most common being SPF 15, SPF 30, and SPF 50. According to the Journal of Clinical and Aesthetic Dermatology (JCAD), SPF values are usually broken up into four main categories: low (SPF 6 to 10), medium (SPF 15, 20, and 25), high (SPF 30 and 50), and very high (SPF 50+), although the US FDA does not recognize these distinctions.2
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Since SPF only applies to UVB rays, it’s essential to choose a sunscreen that says “broad-spectrum” on the label—this indicates that the product helps protect against UVB and UVA rays. Both types of UV rays can damage your skin and contribute to skin cancer. As mentioned above, UVB rays are responsible for causing sunburns. UVA rays, on the other hand, are often referred to as “aging rays” because they can prematurely age your skin—resulting in fine lines, wrinkles, and discoloration. These rays may also damage your skin when you’re indoors.
According to the Skin Cancer Foundation, more than 50% of UVA rays can penetrate glass (whereas UVB rays are largely blocked by glass).3,4 And more than 80% of UVA rays can penetrate cloud cover, according to the American Academy of Dermatology.1 That’s why it’s so important to wear (and reapply) sunscreen every day, even when it’s cloudy or when staying indoors.
The U.S. Food and Drug Administration (FDA) requires all sunscreen products to include an SPF number on their front labels. This SPF rating is determined using a standardized test set forth by the FDA. Sunscreen labels must also indicate whether or not the product has passed the required test to be considered a “broad-spectrum” sunscreen.
Sunscreens with higher SPF numbers will generally offer more protection from UVB rays than products with lower SPF numbers. Let’s use SPF 30 vs. SPF 50 as an example. When you apply a sunscreen with SPF 30, it will help reflect and/or absorb approximately 97% of UVB rays. Meanwhile, a sunscreen with SPF 50 will help reflect and/or absorb about 98% of UVB radiation, per the Skin Cancer Foundation.3 There are also sunscreens that contain an SPF value higher than 50, going all the way up to SPF 100.
Read on to learn more about choosing the ideal SPF number for everyday sun protection.
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There are a few factors to consider when choosing an appropriate SPF value for your daily needs. According to the FDA, only sunscreens with an SPF value of 15 or higher can be considered effective for helping to protect against early skin aging and skin cancer (when used as directed in addition to other protective measures).5 However, the American Academy of Dermatology and the Skin Cancer Foundation both recommend using a water-resistant, broad-spectrum product with an SPF of at least 30 for daily sun protection.1,3 When in doubt, it’s always best to consult a board-certified dermatologist, who can recommend the optimal sunscreen formula and SPF number for your specific needs.
As mentioned earlier, sunscreens that have a higher SPF number generally offer more protection from the sun’s harmful rays. So, does this mean that you should look for a sunscreen with SPF 100 for the best protection? Not necessarily. The FDA says that sunscreens with a higher SPF number may provide greater sunburn protection, but this generally only applies to products with an SPF up to 50.5 The difference in protection between very high SPF numbers (above 50) is actually very small.6
The Skin Cancer Foundation also explains that sunscreens with a very high SPF number may give people a false sense of security, leading them to apply (and reapply) less often or spend more time in the sun.3 Remember: A higher SPF does not mean you can spend more time outside without reapplying.
There may be some cases where an SPF above 50 (such as SPF 100) may be recommended, according to the Skin Cancer Foundation. They advise that high-number SPF sunscreens may be beneficial for those with a family history of skin cancer, certain skin conditions or immune disorders, and people spending extended time outdoors at high altitudes or near the equator.3
To learn more about sun protection best practices for the entire family, head to this article: The Importance of Sun Protection At Every Age.
While the SPF number on your sunscreen label is important, it’s also essential to apply (and reapply) sunscreen correctly—in addition to other sun protection measures, like seeking shade and wearing protective clothing. Here are a few tips to keep in mind when choosing and applying your sunscreen.
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