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Information for the use of sunscreen
2006-07-06
Dear Dr. Proskiw:
I wonder if you would be able to give me some information on the use of sunscreens? There are many sunscreens out on the market today, and my family and I are not sure how to choose them and when they should be applied.
The ancient Greeks used olive oil as a type of sunscreen, however it was not very effective. It wasn't until 1944 that the first effective sunscreen was invented by a pharmacist named Benjamin Green who developed something that would protect soldiers from the sun's harmful rays. This was a sticky, red substance, which worked primarily as a physical block, blocking the sun's rays and prevented sun burns to some extent.
There are some misconceptions about sun protection factor, or SPF as it is known. In theory, the SPF is a multiple that can be applied to the time taken to burn. For example, if toy would burn after 12 minutes in the sun, you'd expect to burn after 120 if you applied a sun screen with an SPF of 10. In practice, protection with a particular sunscreen depends on such factors as the skin type, the amount of sunscreen that is applied and the frequency of application, since sun screen is diluted by perspiration and wiping. Swimming also leads to a loss of sun screen from the skin.
The time of day that the sunscreen is applied and the season also effects protection, since UV radiation varies during the time and day and the season. The SPF is an imperfect measure of skin protection because invisible damage and skin aging are also caused by the very common ultraviolet type A, which does not cause reddening or pain. Conventional sun screen does not block UVA as effectively as UVB. It is my opinion that in using an SPF of 30 on a regular basis, during our hot summer months, is quite effective protection here in the Okanagan Valley. It is best to apply the sunscreen approximately 20 minutes before going outside, and then reapplying approximately 20 - 30 minutes after going outside.
The most harmful rays are between 10:00 am and 4:00 pm, and these are times that people with sensitive skin or a previous history of skin cancer, should avoid being exposed to sun, and if they need to be out in the sun take particular care wearing a large hat or long sleeved clothing.
I've heard that there are some side effects that are possible from using sunscreen.
It is true that some individuals can have a mild to moderate allergic reaction to certain ingredients in sunscreen, particularly the chemical Benzophenone. This is also known as Phenyl Ketone, Diphenyl Ketone or Benzoylbenzene, and it is not clear how much of the Benzophenone is absorbed in the blood stream, but trace amounts can be found in a urinalysis after use.
Most sunscreens work by containing chemical compounds that absorb ultraviolet light or contain an opaque material that reflects light, such as titanium dioxide or zinc oxide, or a combination of both. Typically these absorptive materials are referred to as chemical blocks, whereas opaque materials are mineral or physical blocks. These physical blocks usually have the least amount of side effects and I believe, are most appropriate for our children. I believe that using sunscreen for our children is especially important to prevent long term skin damage and possibly preventing skin cancer in the future.
I hope you enjoy your summer.
Bryan W. Proskiw MD
Diplmate, American Board of Laser Surgery
Director, Canadian Society of Phlebology
Director, Canadian Society of Cosmetic Laser Surgery
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