October 31, 2016

Six Things Everyone Should Know About Sunscreen

St. George Health & Wellness

By Dr. Benjamin Carter

A few months ago, I diagnosed a patient with skin cancer. The patient was accompanied by a family member who asked me, “How can the sun, which is good for us, cause skin cancer?”

The answer to that question is too long to explain in detail in this article, but her question made me think in broader terms about things that are good for us, but can cause damage if exposure is excessive.

Too much thyroid hormone causes hair loss, tremors, rapid heart rate and other health problems. Too much ibuprofen, which can be helpful to treat pain, can lead to kidney failure. Too much calcium can cause abdominal pain, kidney stones, memory loss and bone fractures. All of these things, when produced or consumed in appropriate amounts, are beneficial to our bodies. You can, it would seem, have “too much of a good thing.”

Some things we have control over—such as our consumption of ibuprofen and our sun exposure. Some things we do not have control over—such as our thyroid hormone production (or in my case my chocolate consumption). The things we can control or behaviors we can modify are things we should pay particular attention to.

My patient required surgery to treat her skin cancer. While surgical removal of skin cancer is commonplace for me in my practice, for many of my patients this experience causes anxiety and discomfort.

It is my preference to avoid the sun damage that can cause cancer in the first place, so as to avoid biopsies and surgeries later on. Hopefully the information presented below will help us improve our interactions with the sun and its rays and reduce our risk of skin cancer.

Here are six things everyone should know about sunscreen:

  • SPF stands for sun protection factor – it is based on a sunscreen’s ability to reflect or absorb ultraviolet B (UVB) rays. It has no reference to ultraviolet A (UVA) rays. Both UVB and UVA rays from the sun can cause cancer. There are two ways to think about SPF.

First, SPF is a way to measure how long it will take for someone to get sunburned.

SPF = your time to burn with sunscreen/your time to burn without sunscreen

SPF 15 = 150 minutes to burn with sunscreen applied/10 minutes without sunscreen applied

If it normally takes me 10 minutes to burn (have my skin turn light pink) and I apply SPF 15 sunscreen, it will take 150 minutes for me to burn.

The second way to think about it is based on blocking power as a percentage.

SPF 15 blocks 93 percent of UVB rays

SPF 30 blocks 97 percent of UVB rays

SPF 50 blocks 98 percent of UVB rays

Anything over SPF 50 is likely providing marginal benefit at substantially    increased cost.

  • Not all sunscreens are created equal. The term broad spectrum refers to the fact that a particular sunscreen can block both UVB and UVA rays. However, even amongst broad spectrum sunscreens there are differences. Perhaps the most important thing to understand is whether or not you are using a physical blocker (zinc) or a chemical blocker (avobenzone). They are both effective but physical blockers offer a more complete barrier to UVB and UVA rays. Newer zinc sunscreens can be both effective and virtually invisible. I recommend zinc oxide concentrations above 7%. Some of my favorite sunscreens include Blue Lizard and ELTA MD, which both have zinc concentrations as high as 10% but do not leave my face feeling pasty white. For a daily moisturizer I recommend, Cerave AM.
  • You have to reapply, particularly between the hours of 10AM and 3PM. Some of the blocking ingredients may degrade over 60-120 minutes making reapplication of sunscreen every two hours a must.
  • There is no such thing as waterproof, sweat proof or all day protection when you are talking about sunscreen. In 2013, the FDA issued formal regulations prohibiting sunscreen manufacturers from making these claims. Sunscreens must now use the terms water resistant, sweat resistant and long lasting protection.
  • Vitamin D deficiency has not been associated with sunscreen use. There is some controversy regarding this topic, but to date, the large scale medical studies indicate no significant reduction in vitamin D production following application of sunscreen. This is particularly true for the majority of us who use far less than the recommended amount of sunscreen (recommended amount is one shot glass for full body coverage).   Alternative Vitamin D sources include salmon, eggs, fortified milk and orange juice and oral supplementation.
  • In addition to preventing skin cancer, sunscreens also prevent wrinkling, discoloration of the skin and aging of the skin. Many of these effects are the result of UVA rays not UVB making broad spectrum coverage even more important.

Dr. Ben’s Tips for Enjoying the Sunshine

  • Apply sunscreen 15 minutes prior to exposure
  • One shot glass of sunscreen to cover your body (quarter of a bottle)
  • SPF 30 to SPF 50 – Nothing more, nothing less
  • Sun protective clothing reduces sunscreen applications considerably
  • Remember the high priced real estate – Protect the ears, nose and the rest of the face


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