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The Sun & Ultraviolet Radiation: Sunblocks The sun is responsible for our very existence here on earth. Its light is the fuel for photosynthesis: the process by which plants create their energy and we, in turn, depend on the plants for food and oxygen. The sun's infrared rays keep us warm and its visible rays give us the "light" to see by. The sun's ultraviolet radiation is also useful but, at the same time, its very dangerous to us. Ultraviolet radiation (UVR) is the cause of most skin cancers, many cataracts and 90% of visible aging ( the changes we see in our skin as we get older). UVR is divided into 3 different bands: UVA, UVB, UVC. Virtually all of UVC is filtered out by our atmosphere so that none actually reaches the earth's surface. UVB and UVA both reach the earth in significant amounts. UVB is "stronger" than UVA having a greater ability to cause skin damage. There is , however, about 100 times as much as UVA as UVB so that, despite being weaker, UVA is still dangerous. Some other UVR facts are:
OZONE The ozone layer is located about 30 to 100 Km above the earth. The level of the ozone layer varies according to location and time of year. There is for instance, generally more ozone as you move away from the tropics and more in the winter and spring than in the fall and summer. The ozone layer filters out much of the UVB but has relatively little affect on UVA. It is UVB therefore that will be most affected by any change in atmospheric ozone. Unfortunately, the ozone layer is delicate. The use of Chloroflourocarbons (CFCs) has severely damage the ozone layer. CFCs are released by the use of air conditioners, aerosols, sprays and certain solvents. CFCs released now take about 7 years to get to the ozone layer and do their damage. The average CFC "life span" is about 100 years which means that even after we stop using them, they will be damaging the ozone layer for a long time to come. On the bright side, CFC emissions have decreased drastically over the past few years mostly do the "Montreal Protocol" : a protocol ratified in 1987 and signed by most of the industrialized nations that calls for a 50% reduction in CFC production from 1986 levels by the year 1999. THE SKIN & MELANIN The skin is the bodies largest organ. It makes up about 16% of the total body weight. The skin can be divided into 3 layers. The epidermis is the outermost layer, after which comes the dermis (the middle layer) and then, the subdermis. The subdermis is made up of mainly fat cells, while the epidermis is composed primarily of nerve cells, blood vessels, and connective tissue (more on this later). The epidermis, which is divided into several layers, consists in a large part of Keratin (from the Greek word Keratos, or horn) forming cells. Keratin is what makes the skin tough. Keratin filled cells are formed at the bottom of the epidermis and work their way upward until the mature to form the outermost part of the epidermis (the skin we see and feel from the outside). In this way the top layer of the skin is always shedding and being renewed. The epidermis also has a couple of other cell types that don't migrate to the top but instead, sort of float within the epidermis. The best known of these cells are the melanocytes, which produce Melanin. Melanin is a brown colored protein that helps determine the color of our skin. The difference between the fairest skinned and the darkest people is only a few grams of Melanin. The Melanin that the melanocytes make finds its way into the keratinocytes ( the cells containing the keratin) as they make their way up to the surface. The melanocytes produce more melanin when we are exposed to the sun. The result of this is a "tan". The melanin's job is to help protect us from the damaging UVR. It's important to note however, that a tan is only partially protective. A "good tan" has an SPF of only about 4! A smart way to look at a tan is that the Melanin is the debris left over after the war between your skin and the sun - in other words - there is no such thing as a "healthy Tan" because to get that tan you needed to expose yourself to dangerous amounts of radiation. People who are born with very dark skin are naturally protected more that light skinned individuals but even the darkest people can get skin cancer and most certainly will show the signs of sun related aging (deep lines, sagging skin ..). Also living in the epidermis are cells that are part of our immune system: Langerhans cells. Langerhans cells are there to help ward off invaders such as bacteria. They are also probably involved in recognizing and eliminating early skin cancers. A few minutes of unprotected UVR exposure will damage the Langerhans cells in ways that will last for weeks. In this way the sun delivers a double hit: first it causes damage that can lead to skin cancer then it cripples one of our body's normal cancer defense systems. Below the epidermis is the dermis. The dermis is home to, among other things, collagen. Collagen is the most abundant protein in the body accounting for 30% of your dry body weight. There are 5 types of collagen each with its own characteristics and location: collagen is found in teeth, bone, skin, muscle, cartilage, and many other tissues. In the skin, the collagen provides strength and texture. In the dermis the collagen is formed into a bundle. It looks like a rope, made up of many twined strands. In the young, non sun-damaged skin, the individual strands of the "rope" are separate from each other. As one accumulates more and more sun damage the strands lose their orderly arrangement and, like an old rope, become frayed and tangled. Collagen damaged in this way is no longer strong and supple and this results in the sagging limp skin that we associate with aging. 90%of the changes in our skin that we commonly associate with aging are actually due to sun exposure and could be avoided with proper attention. SUNBURN Sunburn is caused by overexposure to UVR, mostly UVB. In fact, sunburn is almost exclusively a UVB phenomenon. This is important because it means that the SPF system measures UVB protection and not UVA (see SPF below). During a sunburn the skin turns red, swells and, in severe cases, blisters. On a cellular level there is an increase in inflammatory cells as well as many chemicals associated with inflammation. A sunburn continues to develop for 12 to 24 hours after the exposure. One blistering sunburn will double a person's chance of developing skin cancer. Remember however, that avoiding sunburn is not the same as avoiding sun damage. Sunburn is just the immediate sign of UVR overexposure. People who have never been sunburned can still develop the delayed problems such as skin cancer and the sun related skin changes such as deep lines, sagging skin ... . SKIN TYPES The Skin Type system is a method commonly used to assess one's sunburn risk. There are 6 (1 - 6) skin types (see below). The lower numbers represent those people more likely to burn and the higher numbers are reserved for those people with a greater degree of natural protection. As we all know, fair skinned, light eyed people with freckles are the most sun sensitive while dark skinned dark eyed are the least sun sensitive. Everyone else is somewhere in-between. Again, it is important to remember that, while avoiding a burn is important, it does not mean that you have escaped more serious damage that can lead to damaged skin and even cancer. Skin Types
SPF SPF stands for Sunscreen Protection Factor. It is measured by determining how long a given person takes to "burn" with and without the sunscreen product on. If it takes 10 times longer with the sunscreen product then that product has an SPF of 10. If it only takes twice as long then that product has an SPF of 2. In reality, the testing labs don't really burn the test subjects they give them just enough UVR to cause the skin to turn barely red. This minimum does is called the MED (minimal erythemal dose). SUNSCREENS Sunscreens 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 2 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 sunscreen. For example, Benzophenone (Oxybenzone) is an organic screen 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 known to the best sunblock available but it was cosmetically unacceptable and therefor 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's 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 at 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 that 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 an 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! To Purchase Broad and Full Spectrum SunBlocks, click here
Special Thanks to Fitzpatrick's Dermatology in General Medicine as a reference for this page.
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