SPF What?

August 14, 2018

The American Academy of Dermatology recommends choosing a sunscreen that has three key features.

 

1) SPF 30

2) Broad spectrum

3) Water resistant

 

All three of these key features are essential in choosing an excellent sunscreen (and when it comes to the protection of our gorgeous faces, why we would we accept anything less than excellent?!).  So today we are going to talk specifically about key feature number one, SPF.  This is the number that you see on every sunscreen bottle letting you know about the protection power of the product.  Although it seems like the obvious choice when it comes to SPF is the more, the better, that is not necessarily true.  It’s definitely not the whole story.  To get the whole story, let’s break down this very important little number.

SPF is a measure of how much sun exposure protected skin can experience before producing a sunburn vs. unprotected skin. 

 

The SPF number refers to the fraction of UV radiation that is actually reaching your skin.

 

For example:

Unprotected skin = 1/1 or 100%, meaning when your skin is unprotected 100% of solar radiation is penetrating your skin.

Skin protected with SPF 30 = 1/30 or 3%, meaning when your skin is protected with SPF 30 only 3% of solar radiation is penetrating your skin.

 

Another way to think about SPF is to imagine a shower head with 100 streams of water raining down on you.  That is your unprotected (and soaking wet!) skin.  Now imagine that 97 of those streams were covered and only 3 streams were hitting you.  That is your skin protected with SPF 30.  You’re getting 97% coverage, not bad!

 

It’s a common belief that SPF is simply a measure of time.  Based on our above example, you can see that it’s actually more accurate to think about SPF as a measure of the amount of sun exposure, not the duration of sun exposure.  However, amount of exposure will be related to time spent in the sun.  Therefore, in theory, if you could normally stay in the sun unprotected for 10 minutes before getting a sunburn, you would be able to stay in the sun 30 times longer when protected with SPF 30, or 300 minutes (5 hours).  Although kind of true, this belief is misleading because there are so many factors that contribute to how quickly or slowly you are receiving solar radiation.  Because of all the variables, the time it will take a person to produce a sunburn can vary wildly.  Some factors that can contribute to this variance are –

  • Intensity of the sun - It may take a full hour to sunburn at 9:00 am when the sun is less intense but may take only 15 minutes to sunburn at 1:00 pm when the sun is more intense.

  • Cloud coverage – Clouds do not ever block the sun completely (which is why we need to wear sunscreen even on cloudy days) but they can diminish solar intensity.

  • Geographic location - Solar intensity is greater at lower latitudes.

  • Proximity to snow, water, and sand – All three reflect solar rays and can make exposure more intense.

  • Your skin type – Fairer skin is likely to absorb more solar energy than darker skin.

  • Amount of sunscreen applied – Thicker applications are more protective than thinner applications.

  • Frequency of reapplication – Sunscreen becomes less effective over time making a fresh application more protective than an older application.

  • Activities that are likely to rinse or rub off sunscreen – Sunscreen has to be present on the skin in order to protect.  Activities such as swimming, sweating, or physical activity can wear off the product and diminish protection.

A good general rule, regardless of the SPF number, is to reapply every two hours.  You may even want to reapply sooner if you are doing physical activity that could rub, rinse, or sweat off your sunscreen.  You may also go a little longer between reapplications if you’re spending the day indoors (but be mindful of windows because UVA rays can penetrate glass!).

 

Wearing a sunscreen every day (and reapplying regularly!) is the single best thing you can do to protect and preserve your skin.  Hands down.  Sun damage is no joke.

 

We know we want to protect our skin so the next question is, what is the best SPF number?  If SPF 30 is good, what about SPF 1000?  Why not SPF ONE MILLION?!  After all, we don’t want to get skimpy with our sun protection! 

 

Sorry y’all, it doesn’t really work that way.  Although the level of protection does increase as SPF increases, once you pass SPF 30 the additional protection is minimal.  Remember our shower head analogy?  Well, if SPF 30 means that only 3 water streams hit you, then SPF 50 means that only 2 water streams hit you.  Above SPF 50 the added protection is so marginal that the FDA will only allow companies to label products as SPF 50+.  No more SPF claims of outrageously high numbers that aim to make you believe the product is offering superior protection when that is not the case.

 

Some things to remember when choosing the right SPF for you –

  • SPF 50 blocks 98% of UV radiation (2 water streams hitting you in the shower)

  • SPF 30 blocks 97% of UV radiation (3 water streams hitting you in the shower)

  • SPF 15 blocks 93% of UV radiation (7 water streams hitting you in the shower)

  • Products with SPF 15 and lower may prevent some sunburn but have not been proven to prevent skin cancer or premature signs of aging

  • Per FDA guidelines, no sunscreen can claim to offer 100% protection

  • Companies cannot use the terminology “sunblock” on their packaging

  • Companies cannot claim that their product works longer than 2 hours

  • Sunscreens must retain their full SPF for 3 years (it’s a smart idea to throw away any sunscreen past it expiration date, as the protective power has likely diminished)

It seems like a lot to know about a little number, but this is a very important little number!  It can be the difference between healthy skin and skin cancer, youthful skin and wrinkles, even skin tone and discoloration.  Our skin is the largest organ of our body.  It protects us and fights for us against the environmental aggressors we face every day.  Why not help your skin help you (think Cuba Gooding Jr. in Jerry McGuire, “Help me help you!”). 

 

Treat your skin right, take care of it, protect it, and it will reward you with health and happiness every time you look in the mirror!

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