Sunscreen are chemicals that, when applied topically, keep UVR from reaching your skin. They work either by absorbing the UVR or by reflecting it. Either way, if used properly, they can keep a lot of UVR from reaching you. There are two types of sunscreens: organic and inorganic (also called physical). Organic sunscreens have been the mainstay of commercially available products for years. The term «organic» simply means that these sunscreens are composed of, among other things, carbon and hydrogen. It does not mean that they are naturally occurring and, in fact they are not. Organic sunscreens are relatively complex molecules that are to some degree absorbed into the skin.
The most famous sunscreen is PABA (para amino benzoic acid). PABA became so well known because a significant number of people turned out to be allergic to it. Most products are now «PABA Free» but many people still have problems with one or another of the organic sunscreens. For example, Benzophenone (Oxybenzone) is an organic sunscreen that is commonly used. It is probably the one most associated with adverse reactions. Physical sunscreens are actually microscopic solid pieces of sunscreen. Zinc oxide and Titanium dioxide are the two that are commonly used. Most people associate zinc oxide with the white thick paste lifeguards used to use. It was know to be the best sun block available but it was cosmetically unacceptable and therefore used only by lifeguards or skin cancer patients.
Fortunately, things have changed and you can now get physical sunscreens that are transparent. Zinc oxide, for example, is now manufactured so that the particles are so small that you can not see them. These space age physical sunscreens are referred to as microfine powders and Z-COTE (microfine zinc oxide) is an example. The sunscreen manufacturers now use Z-COTE and other microfine powders as ingredients in their sunscreens. Zinc oxide is the primary active ingredient in many baby care products and thus has a very long history of safe use and is not associated with any allergic reactions. Because of this, physical sunscreens, like zinc oxide, are ideal for beach products and for products such as moisturizers and make up that are used every day and need to be as gentle as possible. Most of the organic sunscreens block only UVB. Titanium dioxide blocks some UVA and Zinc oxide blocks more UVR than any other single ingredient. When buying a sunscreen you should get at least an SPF 15 and preferably one that contains zinc oxide. At a minimum, make sure it says «Broad Spectrum».
You should apply the sunscreen about 20 minutes before going out. This gives the sunscreen time to «set up» on your skin so that it can do its job. An SPF 2 blocks about 50% of the UVR. An SPF 10 gets about 85%. An SPF 15 stops about 95% and an SPF 30 stops about 97%. That is why most health professionals agree that an SPF 15 is enough. This all assumes that the sunscreen is applied correctly. When the SPF test is done the testing lab uses an amount of sunscreen representative of 1 ounce per each full body (adult) application. This means that the average 4 ounce tube would last an adult 4 applications at the beach. If you stayed on the beach 4 hours and applied the sunscreen every 2 hours then a tube would last only 2 days (4 applications). Virtually nobody uses this much sunscreen which means more often than not, the sunscreens are being under-applied and people are not receiving the protection they think they are. Some people try to get around this by using a higher SPF but less of it. For instance, it’s appealing to think that if you use a little bit of SPF 30 its really like using an SPF 15. Unfortunately, it doesn’t work that way. There is no good way to predict the SPF of an improperly applied sunscreen so – bottom line – use at least an SPF 15 and use it correctly!