What Is SPF and The Difference In Strengths

Written By: Belinda Stewart

I get this question quite frequently as I practice Aesthetic Nursing.  As summer is approaching and we have become a society that realizes how important it is to protect our skin, understanding this is paramount. 

SPF (sun protection factor) is a relative measure of how long a sunscreen will protect you from ultraviolet (UV) B rays.  The primary cause of reddening and sunburn, UVB rays tend to injure and damage the epidermis, the skin’s outer layers.   Thank goodness looking like a lobster is no longer in.  The epidermis is where the most common (and least dangerous) forms of skin cancer occur. Those cancers are linked to sun-accumulation over the years.  Remember the Iodine and baby oil days?  If you were part of this generation, we are certainly battling the consequences now.  Another type of skin cancer, melanoma, is thought to be caused by brief, intense exposures, such as a blistering sunburn.

Understanding SPF and the number that follows.

Lets now try to understand what the difference between SPF 15 verses SPF 50.  This all-important number allows us to estimate the amount of time you can stay in the sun without getting sunburned. For example, an SPF of 15 would allow you to stay in the sun 15 times longer than you could without protection. So, if your skin starts to redden in 20 minutes without sun block, applying a product with SPF 15 increases that time by a factor of 15, meaning you could stay in the sun for 300 minutes.

Keep in mind that a higher SPF is not necessarily better once you hit the upper limit according to the American Academy of Dermatology.  It recommends choosing a sunscreen with an SPF of at least 30, after that you start to get diminishing returns with an SPF above 50 says Sean Dunn, a One Medical physician assistant on the virtual care team. “Higher number SPFs offer slightly more protection, but also contain more chemicals — and no sunscreen can block 100 percent of the sun’s rays.” Dunn also states that there is no scientific evidence that using a sunscreen with a 50+ SPF is better than sunscreen with an SPF of 50.

But sunscreen is only part of the big picture. A multitude of reasons affect how well you are protected from the sun.  Sunscreen can be easily washed off by water or sweat.  This can leave parts of your skin vulnerable to UV rays. Applying your sun protection unevenly or not reapplying sunscreen often enough can also reduce its effectiveness.  So remember, if you are on the beautiful scenic lake, or working in the yard all day, make sure to reapply your SPF sunscreen and protect yourself from the blistering sun!

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