Almost all skin cancers are caused by excessive exposure to sunlight. Basal and squamous cell skin cancers are caused by cumulative exposure to sunlight over a lifetime, so every time you expose any part of your skin to direct sunlight, you are adding to the damage that you have received from previous exposures. Melanomas are different. They can be caused by a single sunburn at any age.
How UV Rays from the Sun Cause Skin Cancer You replace your skin completely every 28 days. The outer layer of skin cells are constantly being removed as dander or dandruff. New skin cells start at the bottom inner layer of skin and move up toward the outside as you shed the old skin. The new skin cells are formed by reproducing the cells that contain your genetic material, DNA. Cancer is caused by mutations in which the genetic information in your DNA is changed. Ultraviolet light exposure is one cause of these mutations.
What is Cancer? Every cell in your body is programmed to grow for a certain period and then die. This is called apoptosis. Skin cells live 28 days and then die. Red blood cells live 120 days and die, the cells in your mouth live 24 to 48 hours, and so forth. Cancer means that the cells do not die at their programmed time. The genetic material mutates (changes) and the cells try to live forever. The vast majority of skin cells continue on their normal 28-day path, but UV light can damage the genetic material so that the cells forget to die and become cancerous.
Everyone makes millions of cancer cells every day. One of the jobs of your immune system is to search out and kill cancer cells. A healthy immune system prevents most cancers from growing, but for various reasons which we do not fully understand, sometimes cancer cells escape destruction by your immune system and a cancer (i.e., a tumor) begins to grow in your body.
Most types of cancer cells do not kill a person until they spread to other parts of the body. For example, breast cancers do not kill as long as they remain in the breast. However, when breast cancer spreads to your brain, liver or lungs, it destroys these tissues which can kill you. The same is true of skin cancers; they do not become deadly unless they spread to other tissues in your body.
Protect Yourself from Sunlight The most effective protection from UV light is a roof, and then clothes. Sunscreens are the least protective, but they are better than nothing.
Clothes: Clothes are far more protective than sun screens. Wear a hat that covers your ears, a shirt, and arm coolers on your arms when you exercise outdoors. Dark colored fabrics block UV rays better than light colors: The colors that block the most UV include black, deep blue, orange and red. Tightly woven fabrics block more UV than looser weaves: Hold the material up to a light source. The more light that passes through a fabric, the more UV will also pass.
Arm Coolers: We use “arm coolers” that block the sun’s rays and evaporate sweat rapidly to cool our arms at the same time. You can even make your arms feel cold on hot days just by pouring water on them. You can buy arm coolers in sports stores or online.
Sunglasses: Skin cancers around the eyes, mouth, ears and nose are among the most difficult to treat and cure and are also the ones most likely to recur after treatment. Cancers in these areas can tunnel underneath the skin and not be obvious to the naked eye. Sunglasses block UV light and therefore help to prevent cancer in skin around your eyes.
Sunscreens: Remember that sweating, swimming, or a brush of your hand can remove the sunscreen. Apply a sunscreen so you can see it on your skin and then reapply that sunscreen at least every couple of hours. Make sure that you apply sunscreen to the areas with the most exposure to sunlight over your lifetime: the top of your ears, your face, the back of your neck, and your arms and hands. To meet your daily vitamin D requirements from sunlight, you can expose your legs or other areas of your body that have received little cumulative sun exposure over your lifetime.
Sun Protection Factor (SPF) The SPF on sunscreen labels tells you how long it takes to burn your skin underneath that sunscreen. It does not tell you how much protection you are getting. A SPF 30 sunscreen blocks 97 percent of UVB rays, compared to an SPF 15 sunscreen that blocks 93 percent. No sunscreen blocks all UV rays.
Broad-spectrum sunscreens provide some protection against UVA and UVB rays, but the SPF (sun-protection factor) rating refers only to the level of protection from UVB rays. The FDA ruled that sunscreen labels that claim to be “broad spectrum” must protect against UVA as well as UVB. These rules also prohibit any sunscreen from claiming that it prevents skin cancer or aging because no sunscreen blocks all UV rays. Sunscreens cannot claim that they last for more than two hours, unless proof of longer protection is submitted to the FDA.
There is no advantage to choosing sunscreens just because they have an SPF greater than 50. The FDA has shown that you do not need a sunscreen with an SPF greater than 30.
Sunscreen Ingredients Many sunscreens contain the filters octylmethoxycinnamate, benzophenone-3 or octocrylene, which reflect ultra violet rays away from your skin to protect it only when they are on the surface of the skin. However, when these sunscreens are absorbed and the skin is not re-coated, they increase skin production of harmful oxidants that can cause skin aging and cancer (Free Radical Biology & Medicine, September 2009). Reapplying the sunscreen so that some remains on the skin surface can help to prevent this damage.
We do not know how safe sun screens are because they have never been tested systematically. Oxybenzone in sunscreens has been shown to be absorbed into the bloodstream in humans and to disrupt hormones in animals. At this time, it appears that zinc oxide and titanium dioxide-based sunscreens are among the best and safest on the market, but there is some concern about nanoparticles and the FDA does not require testing or disclosure of the particle sizes used.
Recommended Brands and Ingredients Each year the Environmental Working Group posts its findings on sunscreen effectiveness and safety, with brand name listings and recommendations; see http://www.ewg.org/2015sunscreen/
Vitamin D Most people cannot meet their needs for vitamin D unless they expose some skin to sunlight or take vitamin D supplements. Food sources are inadequate and vitamin D pills may not supply all the benefits of sunlight. If you do not allow the sun’s rays to reach your skin, you will not be able to gain all the benefits of sunlight. People in southern climates can usually meet their vitamin D requirements by exposing a small area of skin for about half an hour at mid-day.
Sun Protection Myths
• Clouds do not protect you. Up to 80 percent of the sun’s UV rays can pass through clouds to damage your skin.
• Glass does not protect you. Glass blocks UVB rays that are the primary causes of skin cancer and sunburns, but they do not block UVA that can also cause skin cancer and aging.
• Beach umbrellas do not protect you. UV rays are reflected toward you from sand and water. Studies show that you get up to 84 percent of the exposure to UV radiation under an umbrella that you receive in the open sun.
• Dark skin does not protect you completely. People with dark skin still need to follow sun protection precautions. Skin pigment reduces the amount of UV rays that pass into skin, but it does not prevent sunburns or skin cancer.
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