by Tony Marchand, M.D.

Introduction:
Sunscreens are products combining several ingredients that help prevent the sun's ultraviolet (UV) radiation from reaching the skin. Two types of ultraviolet radiation, UVA and UVB. UVA can damage the skin, age it prematurely, and increase your risk of skin cancer. It's effects may not be seen for years. UVB is the main culprit behind sun burn but may also promote cancer risk. They also exacerbate the carcinogenic effects of UVB. You want to pick a sunscreen that will protect against both.

SPF or Sun Protection Factor is a measure of a sunscreens ability to protect against UVB sun burn. Without sunscreen, one would burn in about 20 minutes depending on a number of factors (water refection, clouds, time of year, etc.). A SPF of 15 is theoretically suppose to prevent sun burn 15 times longer then would be without use. However, this is incorrect. One should look at an SPF of 15 as blocking out 93% of all incoming UVB rays and a SPF of 30 as blocking out 97%. An SPF of 50 theoretically blocks 98% of UVB, but only when applied correctly and often.

Ingredients:
There are two type of sunscreens: UV blockers and UV absorbers.

The blockers stop both UVA and UVB. Zinc Oxide, which you see on the noses of those life guards at the beach is an excellent blocker of both. A newer formulation of zinc oxide or micronized titanium dioxide is not as opaque and provides excellent protection.

UV absorbers include a variety of chemical that absorb UVA and/or UVB to varying extents. Avobenzone tops the list in UVA absorption and has the fewest allergic reactions. The downside is that it breaks down by 50-90% in sun light within an hour. Some UVB absorbers like OMC and octocrylene help stabilize Avobenzone. A number of other chemicals are good UVB absorbers such as oxybenzone and sulisobenzone (which also has some good UVA absorption, however, can be irritating and are not water resistant) and PABA derivatives, salicylate's, and/or cinnamates (octylmethoxycinnamate) which also can be irritating in some individuals.

Safety:
The safety of the chemical used above is "hotly" debated. Stanford's Dr. Swetter states: “Currently marketed sunscreens are deemed safe and effective by the FDA in preventing skin aging and skin cancer when used appropriately.” Yet a 2013 article published in The Washington Post quotes Robert Friedman, Clinical Professor of Dermatology at the New York University School of Medicine, who explained gray areas in research remain. “Even though the data are soft, we do know that a certain amount of the chemical sunscreens are absorbed into the body, and we don't know exactly what their effects are,” Friedman told the newspaper.

Myths:
  • If it's cold or cloudy outside, you don't need sunscreen. False. Up to 40 percent of the sun's ultraviolet radiation reaches the earth on a completely cloudy day. This misperception often leads to the most serious sunburns.
  • Spray sunscreens give the best coverage. True if used correctly but it can be hard to judge how much your getting and areas missed by the spray. So overall, I give this a False. If using a spray, spray it on your hands then apply to face and other areas. Consumer Reports notes that all spay sunscreens are flammable so be careful were you use and store them.
  • A little goes a long way. False. Most people use about 2 tablespoons of sunscreen for application when at the beach to cover the face and body. You need more then twice this amount per application. Don't forget to apply 15 to 30 minutes before sun exposure.
  • Sunscreens deliver the SPF listed on the bottle. False. This has not been found to be the case as shown in Consumer Report's testing. In addition 18 of the 20 sunscreens tested by Consumer Report did not provide the SPF listed on the bottle after exposure to water. So reapply after taking each dip.
  • An SPF of 30 provides twice the protection of an SPF of 15. False. SPF 15 filters out approximately 93 percent of all incoming UVB rays. SPF 30 keeps out 97 percent and SPF 50 keeps out 98 percent. An SPF of 50 (or higher if you prefer) is sufficient. But the trick is to apply enough and reapply every two hours. Also use hat and clothing for added protection.
  • Kids need a special sunscreen. False. The FDA makes no distinction for children versus adults.
  • I'm older now and most of the cancer causing affects of the sun come when you're a kid, so I don't have to worry about sunscreen. False. The carcinogenic effects of the sun can come at any age, so protect your self.
  • Sunscreens do not expire. False. Most sunscreens have an expiration date of about 3 years and is listed on the bottle. However, if the bottle has been lying around in the heat much of the summer or in your hot car, the active ingredients break down. Some physicians say if you haven't used up your bottle of sunscreen in a year, your applying to little each application.
Best Sun Screens Protection:
My recommendations: Use a sunscreen with an SPF of at least 30. Although my favorite contains zinc oxide for best UV blockage, Consumer Report, as of this printing, shows those with a UVA absorber such as Avobenzone and a combination of UVB absorbers Octocryele (which helps stabilize Avobenzone), Homosalate, and Ocisalate top the list.



Remember, there is no sunscreen that blocks all UV and all sunscreens must be applied correctly and often. Don't rely on sunscreen alone but as stated above: "make them part of a sun-protection strategy that includes clothing and seeking shade."

References:
  1. Sun Screens Explained   Skin Cancer Foundation
  2. Drugs & Medications - sunscreen topical   From WebMD
  3. Sunscreen: How to Choose   Advise from REI with the following contributors: Brian Adams, MD, MPH and Interim Chairman of the Department of Dermatology at the University of Cincinnati School of Medicine; Robert Friedman, Clinical Professor of Dermatology at the New York University School of Medicine; Susan M. Swetter, MD, Professor of Dermatology and Director of the Pigmented Lesion and Melanoma Program at Stanford University Medical Center; John E. Wolf, Jr., MD, MA and Professor and Chairman of the Department of Dermatology at the Baylor College of Medicine in Houston.
  4. Proper Use of Sunscreen   from About.com Dermatology
  5. Sun Block   from the University of California, San Francisco 06/10/2011
  6. Sunscreen   from ConsumerReports.com 06/11/14