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www.skincancer.org/skin-cancer-information/ask-the-experts/does-a-higher-spf...

Does a sunscreen with a high SPF (sun protection factor) protect skin better than one with a lower SPF? ... A sunscreen’s SPF number refers mainly to the amount of UVB protection it provides. ... That may seem like a small difference until you realize that the SPF 30 is allowing 50 percent more UV radiation onto your skin.

health.howstuffworks.com/skin-care/beauty/sun-care/spf.htm

SPF, or sun protection factor, numbers were introduced in 1962 to measure a sunscreen's effect against UVB rays. To determine a sunscreen's SPF, testers round up 20 sun-sensitive people and measure the amount of UV rays it takes them to burn without sunscreen.

www.verywellhealth.com/what-is-spf-1068889

SPF stands for sun protection factor. Simply put, an SPF rating tells you how long you can stay in the sun without getting burned while wearing that sunscreen, compared with how long you can stay in the sun before you burn without wearing that sunscreen. For example, if it typically takes you 15 minutes to burn without sunscreen and you apply an SPF 10, it will take 10 times longer (2.5 hours ...

www.webmd.com/beauty/features/high-spf-sunscreens-are-they-better

High-SPF Sunscreens: Are They Better? ... "SPF is not a consumer-friendly number," says Florida dermatologist James M. Spencer, MD. ... concedes that the difference in sunburn protection between ...

www.freepeople.com/sunscreen-debate

SPF 30 is the most common level for most people and skin types. No sunscreen can block all UV rays, but what we do know is: SPF 15 blocks 93% of UVB rays, SPF 30 blocks 97% of UVB rays and SPF 50 blocks 98% of UVB rays. So, the difference between 30 and 50 is about 1 percent.

www.youtube.com/watch?v=rXzUq3ljUaM

"What Is The Difference In SPF Numbers? Watch more videos for more knowledge What Is The Difference In SPF Numbers? - YouTube https://www.youtube.com/watch/r...

www.reference.com/beauty-fashion/difference-between-spf-30-spf-50-6843c42a4aa12eba

What Is the Difference Between SPF 30 and SPF 50? Higher SPF ratings generally mean better protection from the sun's ultraviolet B rays, so SPF 30 sunscreens provide protection from 97 percent of UVB rays and SPF 45 or higher sunscreens block 98 percent.

news.psu.edu/story/141338/2010/06/01/research/probing-question-what-does-spf...

"The SPF numbers are not exact, and results vary by individual, since some skin types burn faster than others." Another factor to consider is protection from UVA rays. These might not cause a visible sunburn, but they can still damage tissue and cause wrinkles, and they penetrate deeper into the skin than UVB rays. ...

www.skincancer.org/prevention/sun-protection/sunscreen/sunscreens-explained

SPF 30 keeps out 97 percent and SPF 50 keeps out 98 percent. They may seem like negligible differences, but if you are light-sensitive, or have a history of skin cancer, those extra percentages will make a difference. And as you can see, no sunscreen can block all UV rays.

www.ewg.org/sunscreen/report/whats-wrong-with-high-spf

Theoretically, applying sunscreen with a sun protection factor – SPF – of 100 would allow beachgoers to bare their skin 100 times longer before suffering a sunburn. Someone who would normally redden after 30 minutes in the midday sun could stay out for 50 hours. But for high-SPF sunscreens, theory and reality are two different things.