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The media are full of information about the effects of too much sun exposure. Unfortunately, most people still link sun exposure to sunburn and only use protection when planning a full day of outside activities. As with most health issues, it is the years of daily short exposures that add up to the most sun damage. Just 10 minutes a day add up to over an hour of unprotected sun exposure in just one week. What about commuting or just running errands? If you thought UV rays couldn’t find you in your car, think again. While the windshield in most cars is very effective at screening UV, the rest of the windows only absorb a portion of the ultraviolet spectrum. Scientists used to think that the portion of the ultraviolet light that is transmitted through glass was "safe" ultraviolet but research continues to uncover the damaging effects of this higher wavelength UV. Still not a believer? Would you leave your dry-cleaning hanging in the car for a month? Most people wouldn’t dream of leaving valuable clothing in a vehicle in case of damage. Yet, we drive for years without considering what may be occurring inside the skin where the damage won’t be seen until it is too late to repair.
Without radiation from the sun, life on the Earth would cease to exist. Sunshine is essential to plant and animal life but there are certain portions of this radiation that the human body could use in much smaller doses. Solar radiation is a form of electromagnetic radiation. Electromagnetic energy exists as waves. The length of one cycle of those waves is called a wavelength. These wavelengths are measured in units of nanometers (nm), or one billionth of a meter. Different types of energy are distinguished by their "wavelength."
Scientists have split the solar energy from the sun into three bands of wavelengths. These three bands are: Ultraviolet (100-380 nm), Visible Light (380-780 nm), and Near Infrared (780-2400 nm). As its name implies, visible light is the light that the human eye can see. Since individuals vary in their ability to detect visible light, the borders surrounding the visible light region are somewhat artificial. Near infrared radiation is the part of the sun’s rays that warm the Earth. Ultraviolet is energy from the sun that we can neither see nor feel but these short wavelengths can have a tremendous effect on the human body.
Although ultraviolet light accounts for only 3% of the total solar spectrum, it is the most active part of the spectrum for photodamage. Photobiologists, scientists who study the effects of light on living things, have divided ultraviolet radiation into three groups of wavelengths. UVC (less than 280nm), UVB (280-320 nm), and UVA (320-380 nm). All UVC and a portion of the UVB radiation is screened by the earth’s ozone layer. UVB is screened completely by glass and many types of plastic glazing. UVB is most commonly known as the part of the UV spectrum that causes sunburn and is more potent than the longer wavelength UVA. UVA is not screened by glass and until recently sunscreens did not screen in the UVA region. Most sunscreens still provide very little UVA protection. While UVB is more potent, UVA makes up over 90% of the ultraviolet radiation that reaches the earth’s surface. The total amount of UV that reaches the earth’s surface varies by season, time of day, and geography. It is highest during summer, midday, and at the equator. It is important to understand that all ultraviolet light is not the same and that different wavelengths of UV may have varied effects on the body.
Most of the important functions of the human body happen inside our outer protective layer. In animals this protective skin layer is further covered by fur or hair, but people have very little natural protection for the skin. Few people realize that the skin is the largest organ of the body. The skin is made up of an outer layer called the epidermis and an inner layer called the dermis. The epidermis is in a constant state of renewal. The top layer is in fact composed of flat dead skin cells and is known as the stratum corneum. These cells are shed in microscopic flakes in approximately four-week cycles. New living cells from the bottom of the epidermis are constantly being formed and move toward the surface to repeat the cycle. The epidermis protects the body from bacteria and moisture loss.
The dermis layer lies below the epidermis and is up to forty times thicker. The dermis is composed of collagen and elastin fibers that provide support for the blood vessels, nerves, sweat glands, hair follicles, and sebaceous glands that are all a part of healthy functioning skin. Collagen and elastin fibers are important because they help the skin maintain its elastic properties. Damage to this layer leads to sagging and wrinkling of the skin. Fibrocytes, the cells that produce collagen fibers are also found in the dermis. At the interface between the dermis and epidermis are found the melanocytes. These cells contain the pigment melanin that gives skin its color.
The only other human organ that is exposed directly to the sun is the eye. While we have eyelids and eyelashes that offer some protection from dust and light, the eye is generally exposed to all forms of light, especially in young children. The viewing area of the eye is composed of the outer protective mucus membrane, the cornea, the aqueous humor, the iris, the pupil, the lens, the vitreous humor, and the retina. Damage can occur to the lens and the retina by exposure to sunlight. Young children are especially susceptible to retina damage since the lens does not develop its full potential to screen ultraviolet and blue light until adulthood.
The media are flooded with information about the need to wear sunscreen, but few people understand the science behind those warnings or the consequences of ignoring them. Ultraviolet radiation has been shown to contribute to all three major types of skin cancer, photoaging of the skin (including wrinkling, pigment changes, and sagging), photosensitivity causing rashes and inflammation, and eye damage including partial blindness and cataracts. There is new research which indicates that ultraviolet radiation may in fact take away some of the body’s natural immunity in subtle and specific ways.1
The most recent statistics predict the future skin cancer rate will be a million or more cases per year in the United States alone. At that rate one in six Americans will develop skin cancer during their lifetime according to the report2. (As of 2005, the rate is calculated at one in five.) There are many theories for this increase but whatever the reason the number of cases is rising. While scientists do not know the exact reason for the increase, they are certain that skin cancer is linked to sun exposure.
Cancer is a group of diseases with one thing in common: cells become abnormal, dividing too often and without control or order. These malignant cells form a tumor that can invade and destroy nearby tissue. The cancer cells also can spread throughout the lymphatic system or the bloodstream to other parts of the body and form new tumors. The spread of cancer is called metastasis.
There are three types of skin cancer. The two most common types are basal cell carcinoma and squamous cell carcinoma. These two types account for over 90% of the skin cancer diagnosed in the United States. These are slow growing cancers that seldom spread to other parts of the body. Skin cancers of this type are the most curable. It is currently believed that these types of skin cancer are linked mainly to UVB exposure although UVA is now being studied as well.
The most deadly form of skin cancer is melanoma. Unlike the other two forms of skin cancer, malignant melanoma can quickly spread to other parts of the body if not treated early. There were 35,000 cases of malignant melanoma in 1995 and the number of cases is increasing at 4% per year3. Up until recently, it was believed that melanoma was also caused predominantly by UVB. Research at the M.D. Anderson Cancer Center in Houston, Texas, has indicated that while using sunscreen did prevent non-melanoma skin cancers, the sunscreen (which screened mostly in the UVB) had no effect in preventing melanoma. Further evidence of UVA effects came from a study of tanning bed users conducted in Sweden by researchers at University Hospital in Lund. The results were published in the American Journal of Epidemiology, October 1994. Tanning beds use UVA radiation to give users a supposedly "safe" tan. The study found that tanning bed users under the age of 30 who used tanning beds more than 10 times a year had more than seven times the risk of melanoma. At the current rate of increase of melanoma, that would raise the risk for tanning bed users to about 1 in 13. This research along with other studies makes the case against UVA rays so great that the American Medical Association again recommended (in December 1994) that tanning beds be banned for anything but medical use. While no one is sure how UVA radiation effects the skin, some researchers believe that it lowers the immune system’s ability to function properly4.
Most people believe that as we get older our skin naturally begins to wrinkle and sag. While that is true to some extent, scientists believe that as much as 80% of these signs of aging are in fact due to sun exposure. Photoaging is characterized by wrinkles, coarsening, dryness, loss of elastic behavior and pigment changes. The most important change in the skin occurs in the dermis where the elastin fibers, which should be linear, become thickened and tangled and eventually progress into a single mass of non-elastic material. This severe deterioration of the elastin fibers is not seen in sun-protected skin. UVA radiation goes deeper into the skin and will cause elastosis more deeply in the dermis than UVB radiation. The effects of ultraviolet exposure are cumulative and take years to become apparent. In addition to wrinkles, many of the pigment changes associated with aging skin are related to sun exposure. Liver spots, moles, and white patches are all related to getting too much sun. Because children and teenagers spend so much time out in the sun, it is estimated that as much as 80% of UV induced photoaging may occur within the first 20 years of life. There is additional new research that indicates that young skin may be more susceptible to solar damage than older skin. Babies are especially vulnerable to damage from ultraviolet rays.
Photoaging is reversible to some extent and proper screening of ultraviolet rays can improve the skin, but the best defense is prevention. Dermatologists agree: there is no such thing as a "safe" tan from the sun or a tanning bed.
The most commonly used term to describe the symptoms of photosensitivity is "sun poisoning." Photosensitivity usually manifests itself as a rash or skin reaction to some form of solar radiation. People who have never been photosensitive may experience these symptoms while using certain drugs such as tetracycline, sulfa, or chlorpromazine. Eating certain foods such as limes in combination with sun exposure may cause a reaction in some people. Perfumes and other skin products may also cause a reaction. Many photosensitive people react to UVA rays and most sunscreens will not alleviate the reaction.
Some of the more severe photosensitive reactions take place in people with lupus. Somewhere between 40-60% of lupus patients are photosensitive and some are extremely sensitive to ultraviolet light from any source. In addition, many lupus patients have difficulty wearing sunscreens because they cause their own skin rash.
The most severe form of photosensitivity is xeroderma pigmentosum, a rare hereditary disease. XP patients, are so sensitive to ultraviolet rays that they develop skin cancer usually before the age of ten. Their skin is incapable of repairing the DNA damage that is done to the skin with each exposure to ultraviolet radiation. Normal skin can repair this DNA damage to some extent so it may take fifty or sixty years to see the same cancer develop.
As the only other organ exposed to the sun, the eye is also prone to damage from its rays. When ultraviolet rays enter the eye they can damage the protective conjunctiva membrane, the cornea, the lens, or the retina. The most permanent form of eye damage is solar retinopathy that is caused by gazing directly into the sun. While this may be reversible, it can also lead to permanent loss of vision. The damage is caused by visible blue light and UVA. The prevention for this is the age-old adage: Never look directly at the sun!
Other forms of retina damage can also occur from common exposure to sunlight. Infants, children, and teens are more susceptible to damage from ultraviolet radiation. While the cornea absorbs any radiation below 295nm, the lens slowly develops its ability to absorb UVA and blue light reaching its full absorption ability at adulthood.
Unfortunately, since the lens develops into a good UVA absorber, it is susceptible to damage caused by too much UV absorption. Since the lens cannot shed damaged cells there is no way for it to repair itself. This damage often leads to cloudy vision and a condition known as cataracts.
Skin cancer, sunburn, pigment spots, rashes, cataracts, retina damage, and wrinkles have all been linked to exposure to ultraviolet radiation. While scientists work on ways to repair this damage, the best possible defense is prevention. It is never too late to start protecting your skin and eyes from UV damage. Ultraviolet screening techniques and limiting sun exposure can prevent further damage and in some cases the damage may be reversible with proper protection. Living in the dark would be as unhealthy to mental well-being as basking in the sun is to the skin and eyes. Using common sense and taking advantage of the ultraviolet screening techniques available will help protect you and your family from the damage caused by the sun’s UV rays.
One of the times when people are at the highest risk to UVA exposure is when they are in an automobile. Long periods in a glass enclosed area and the closeness of the driver and passengers to sun-drenched glass create a dangerous vulnerability to UVA rays. Automobile glass reduces UVB rays but does not screen out UVA rays; the band of ultraviolet rays that has been linked to melanoma skin cancer. UV screening film will also reduce heat entering the vehicle and thereby reduce heat build up. To protect against excessive repeated exposure to UVA while in a vehicle, UV screening film is a must.
These tips may sound overwhelming, but they easily can become habit. Sunscreen application will soon be like shaving or applying make-up. Sunglasses are already widely used and wide-brimmed hats in many styles are available in stores everywhere. The easiest tip of all may be the installation of UV screening film on your vehicle. Once done, you can forget about it. The film will be working whenever you or your family uses the vehicle. Remember that small doses of UV every day will add up to years of sun exposure. Don’t hide from the sun; just learn to enjoy it safely.
Notes:
1. Cancer Researcher Weekly, April 11, 1994, p 7 (2).
2. U.S. Department of Health and Human Services, Centers for Disease Control and Prevention
3. The University of California, Berkeley, Wellness Letter, June 1994
4. Cancer Researcher Weekly, April 11, 1994, p 7 (2).
For information on Lupus and ultraviolet light, visit this web page: www.lupuscanada.org/html/sun_protection_in_lupus.html
For information on Xeroderma Pigmentosum visit this site: www.xps.org/research.htm#BEYOND