SEBORRHEIC DERMATITIS, DANDRUFF, OILY SKIN PSORIASIS ROSACEA SUN SCREENS SCABIES Selected papers Medical news Members Membership Webwatch Skin Care Dermcalender Cases Text Letters Journals Organizations Foundations General Sites Quiz
Every day we are asked by patients and website visitors about sunscreens. The question most commonly asked “what is the best sunscreen?” The truth is there is no perfect sunscreen, but newer formulations with combinations of ingredients are providing better and better protection. If you are confused by the hundreds of sunscreens that are on the market, you are not alone!
The wavelengths of light that damage the skin are in the ultraviolet range. UV radiation,100-400 nm, comprises three wavebands,UVC(200-290nm), UVB(290-320nm) and UVA(320-400nm).
UVA has two effects. The short term effect is tanning and the long term affect is aging. UVA penetrates into the deeper layer of the skin where it breaks up the elastin and collagen fibers. These are the fibers that give the skin its integrity and elasticity. When this material is damaged the skin becomes wrinkled. In addition, we now also know that Ultraviolet A suppresses the immune system of the skin, possibly making it more susceptible to the development of skin cancer and/or certain types of infections.
The short term effect of UVB is to cause sunburn and the long term effect is skin cancer.
In order to provide optimal protection for the skin, a sunscreen should provide protection against both UVA and UVB.
Radiation intensity is increased by reflection from snow(85%), sand(25%), and water(5%), decreased only somewhat by cloud cover(20-90%) and passage through water(60% after 50cm path length), and unaffected by heat, cold, wind and visible light. It must also be remembered that the intensity of ultraviolet lights of both types becomes more intense the closer one travels to the equator. Also, at high altitudes in places such as ski resorts ultraviolet light is more intense. the damage caused by UV light is not caused by heat. So you can sustain sun damage on a cold but sunny day.
A sunscreen contains a chemical that absorbs the energy of the ultraviolet light, thereby protecting the skin. A sunblock on the other hand reflects the sunlight and actually physically blocks the radiant energy and prevents it from reaching the skin.
When sunscreens first came out in the late 60’s (compounds containing paraminobenzoic(acid etc.) they contained chemicals that filtered out UVB. This was good in that it protected people from sunburn and also reduced their risk of getting skin cancer. The problem was that people then began to spend more time in the sun than they might otherwise have, and exposed themselves to ever increased quantities of UVA. Thus inadvertently the availability of UVB filtering sunscreens may have contributed to premature aging of the skin by prompting people to spend more time in the sun than they might otherwise have.
The main UVB absorbers are: aminobenzoates, cinnamates and salicylates. You will note that these compounds tend to end with the syllable “-ate”. And the best anti UVA sunscreen is methylanthranilate, also known as butylmethoxydibenzoylmethane, avobenzone or Parsol 1789. Other compounds that provide some protection against UVA include oxybenzone, sulisobenzone and dioxybenzone. These compounds tend to end in the suffix “-zone” (unless the name methylanthranilate is used, which it usually isn’t.)
We can sum this up by saying that the “-ates” protect against sunburn and skin cancer and the “-zones” protect against premature aging. You need the “-ates” in the summer and the “-zones” all year round.
Look for the word “broad spectrum” on the label. The other thing that you have to know is that a different rating system is used for UVA protection. The PF factor gives you information about the degree of protection that you will have against UVB. The measure of UVA protection is expressed by the "A" Protection Factor (APF). The APF is not listed on sunscreen labels at present, but one could hope that this information will be provided to consumers in the near future.
Finally, we come to the sunblocks. The best sunblocks contain titanium dioxide and/or micronized zinc oxide. They should be present in concentrations of 1 to 3%. Because these are blocks and not screens, they provide excellent broad spectrum protection.
You can see that for true “broad spectrum” coverage (i.e. protection against most UVA and UVB) a combination of ingredients might be required. Some of the more advanced preparations will contain some of the UVB sunscreens, an anti-UVA (avobenzone being the best) and/or a sunblock (zinc oxide or titanium dioxide).
Finally, the sunscreen must be properly applied:
A sufficient quantity must be used. An adequate amount must be applied evenly. The Food and Drug Administration recommends that 1,000 microliter be applied per 50 square centimeters of skin. What does this actually mean in practical terms? The average adult face has an area equal to a piece of typing paper (try draping a piece of typing paper over your face and you’ll see that I’m right.) That translates into about 810 to 820 square centimeters. That in turn would translate into 1.6 cc of sunscreen for the face. A teaspoon equals 5cc. If you were to be on the safe side and apply 2cc you would be applying about 4/10 of a teaspoon of sunscreen to cover an area the size of your face. Don’t assume that the PF or APF can be doubled by applying a second layer of sunscreen. Twice as much sunscreen isn’t going to turn a sunscreen with a SPF factor of 15 into a sunscreen with an SPF of 30. Recognize that sunscreen can be removed by perspiring or swimming. For best results, a sunscreen should be applied 30 to 60 minutes before venturing into the sun. The crucial times for sun protections are midday from 9 a.m. to 3 p.m. Recognize that the rotation of the earth and the position of the sun in the sky is not influenced by daylight savings time. When your clock set to daylight savings time says it’s 3 p.m., it’s really 2 p.m. Sunscreen reduces the damage that is caused by the sun to the skin. It does not eliminate it. You still should stay in the shade as much as possible and use other protective devices such as hats, sunglasses and clothing.