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The Princeton Longevity Center Medical News

Is Your Sunscreen Doing More Harm Than Good?
How To Choose the Right Product

Summer is upon us and with it comes sunburns.  If you believe the marketing hype, slathering on a layer of sunscreen will protect your skin from damage and the risk of skin cancer.  In fact, many tanning products may actually end up increasing your risk of skin cancer and contribute to aging of your skin.  There are ways to safely enjoy the summer sunshine but picking the right type and level of skin protection is the key.

It is the ultraviolet light present in sunlight that causes tanning, burning and damage.  The ultraviolet spectrum is arbitrarily divided into the UVA and UVB portions.  In general, the UVB rays mainly cause sunburns.  The UVA rays are more dangerous and can cause genetic damage to the skin that leads to skin cancer, including melanoma, and premature aging of the skin.  If you don't want wrinkles, you need to avoid UVA exposure. Most sunscreen products are effective at blocking UVB but most do not offer adequate protection against UVA.  Because blocking UVB means you can stay out in the sun all day without burning, choosing the wrong sunscreen may unwittingly increase your exposure to UVA and do more damage than if you had quickly burned and gotten out of the sun.

There are several ways to limit your UVA exposure.  Of course, the most effective of all, and the one most of us are least likely to do in Summer, is to limit your sun exposure time.  Stay in the shade.  Wear light colored clothing and a hat whenever possible.  Remember that clouds do not offer much of a UV block and it is still possible to damage your skin even on days when the skies are moderately overcast.  Being on or near water increases your exposure as UV will reflect off the water.

If you are out in the sun, you need to use a sunscreen. Some sunscreens contain physical sunblockers.  Others use chemical sunblock.  The two commonly used physical sunblocks are Titanium Dioxide and Zinc Oxide.  These are very effective at blocking both UVA and UVB.  These are particularly useful for individuals with sensitivity to chemical sunblocks.  They are very unlikely to cause skin irritation or allergies.  However, they are also very visible.  Titantium Dioxide is bright white and most people would find it esthetically unacceptable to use a physical sunblock in high concentration over a large area of the body.

Chemical sunblocks work by absorbing UV light.  There is no single ingredient that blocks the entire UV spectrum so you need a sunscreen that combines at least two chemicals to provide "broad spectrum" protection..  Sunscreen ingredients are just starting to catch up with the discovery of how bad UVA rays are for your skin and some of the claims on the label are not reliable.

In the USA, sunscreen products generally list their SPF (Sub Protection Factor) as a guide to the relative strength of the product.  Theoretically, if an individual would normally start to burn after 10 minutes of exposure, applying an SPF of 15 would allow them to increase their exposure time to 150 minutes before starting to burn.  In reality, the degree of protection varies greatly depending on several factors.  But since burning is more related to UVB than UVA exposure, SPF does not reflect the level of protection against skin aging, wrinkling and cancer. It applies only to sunburn.  Your best bet is to carefully check the label on your sunscreen to look for the ingredients that offer protection against both UVA and UVB

The majority of chemical sunblocks will protect only against UVB.  Unless the product contains Avobenzone (also called Parsol 1789) or Mexoryl SX (or Tinosorb outside the U.S.), you're not fully protected from UVA. 

Mexoryl SX is the most effective UVA-blocking ingredient currently available. It has been used in Canada and Europe since 1993, but was just approved by the FDA for use in the U.S. in July 2006. Currently, only a few products are available in the USA with Mexoryl.  L’Oreal holds the exclusive rights to Mexoryl SX.  It can be found in LaRoche-Posay Anthelios SX, a facial moisturizer, and the more widely available Lancôme UV Expert 20, a face and body lotion. If you want the best possible protection, Lancôme UV Expert 20 offers an ideal mix of ingredients, but it's very expensive.

Avobenzone is available in a wider array of less expensive products.  Many products contain a similar component, Oxybenzone.  These will often state on the label that the product protects against UVA.  However, there are actually two kinds of UVA rays -- short and long waves. Oxybenzone offers protection against short-wave UVA but not long-wave UVA.  The long-wave UVA may be the more dangerous.  Avobenzone protects against long-wave rays. Unless your sunscreen also contains avobenzone, zinc oxide, titanium dioxide or Mexoryl SX, you are not protected against long-wave UVA rays. That's why skin-care experts say you should look for "broad spectrum" UVA and UVB protection.

No matter what sunscreen you use, applying it properly is even more important.  We recommend that you use an SPF of at least 30.  A water-resistant sunscreen will be more effective at maintaining your protection if you swim.  You should apply sunscreen at least 15 minutes before sun exposure.  Some chemical sunblocks are slightly absorbed into the skin where subsequent sun exposure can cause the sublock to release free radicals that damage the skin.  Many experts recommend re-applying your sunscreen after 1-2 hours to maintain protection and reduce free radical production within the skin.

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