Skin Health, Sun Protection/Damage
Sun and Light Skintelligence: Above SPF 15 Pointless?
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Number Crunching

I heard that SPFs over 15 are pointless, and anything above SPF 30 is no better than 30 … why should I use sunscreens with higher values?
 
“SPF”, or Sunburn (previously “Sun”) Protection Factor, refers to a product’s ability to protect against UVB light, still the main cause of sunburn. SPF 15 already provides 96.7% protection; SPF 30 yields just 1% more. At SPF 50+, it is presumed that 100% protection from sunburn due to UVB is given. But these values are greatly impacted by the following:

  1. SPF testing is done with 2 mg of product per centimeter square of skin. That’s about a shot glass-full of sunscreen for the body — about 2/3 a teaspoon just for the face and neck. In reality, most people use only 20-50% of this quantity when applying sunscreen.
  2. Most people do not reapply every 2 hours or after swimming, as advised by the American Academy of Dermatology (AAD), to combat the possible loss of protection due to movement, friction, washing off, absorption deeper into the dermis, etc.
  3. Many people go outdoors from 10AM-4PM, when the AAD advocates sun avoidance.

 
All of these practices are the norm, not the exception. So in actual use, a product may be delivering less than its tested SPF (as little as just 12%!).

“It has long been assumed that applying half the recommended ounce meant half the SPF protection. But a small 2007 study published in the British Journal of Dermatology** found that under-application made SPF coverage fall much more steeply…It turns out that if you apply half the amount, you get the protection of only the square root of the SPF.”

SPFs of 50+ can help counteract this effect. As the values are higher, even given the inconsistencies in real-life sunscreen application and other poor sun practices, higher-SPF sunscreens stand a better chance of being able to provide protection at an adequate level. Higher SPFs can help assure protection factors closer to the actual tested numbers and to the important numbers of 30 and up.
 
Often (although not always), higher-SPF products also provide a broader range of protection. SPF values can be pushed up by ingredients with protection effects that go beyond UVB into the UVA and Visible Light (VL) range. UVA and VL effects are less immediately noticed (but can be more deadly) because they do not cause sunburn but chemical reactions in the skin. They also augment photodamage that can, in time, lead to skin aging, hyperpigmentations, cancer, and immunosuppression. Higher SPF values can help assure protection of the skin from the longer light rays that may not burn, but that also damage skin. This is the case with Armada which provides protection against UVB as well as UVA, Visible and Infrared light rays.
 
A concern with high SPFs has been that some people may develop a false sense of security and think they can stay out in the sun all day. If you’ve ever wondered why our labels have so much data and why we spend so much time and effort on our informational literature, this is one reason: we are committed to providing as much information as possible to help people use our products correctly, including the sunscreen use guidelines of the AAD.
 
Inasmuch as they offset imperfect real-life sunscreen use — and can widen the spectrum of protection — higher protection values are a form of risk management.

STILL: WHEN USING SUNSCREEN, REGARDLESS OF THE VALUES, APPLY AN ADEQUATE AMOUNT AND REAPPLY EVERY 1 TO 2 HOURS.
 

*  http://www.nytimes.com/2009/05/14/fashion/14SKIN.html?pagewanted=2&_r=1&th&emc=th 
** Faurschou, A. and Wulf, H.C. “The relation between sun protection factor and amount of suncreen applied in vivo” British Journal of Dermatology 156 (2007): 716–719