According to the National Cancer Institute, cancer is now the second leading cause of death in the United States (NCI, 1995). It is slowly catching up to heart disease, the leading cause of death currently. With nearly one million cases of skin cancer alone expected in the United States this year, it has become the most common kind of cancer (Strange, 1995). The prevalence of skin cancer has prompted much research on the cause and possible prevention of the disease. Ultraviolet radiation has been found as the primary cause of skin cancer. Research has now shown how ultraviolet light penetrates the ozone layer and affects our skin. The purpose of this paper is to inform all of its readers of the harmful effects of sunbathing and neglecting to use sunscreen. Hopefully, it will cause people to be careful when in the sun. Ultraviolet radiation is damaging and must be studied in order to reduce the number of people that acquire skin cancer.
    Ultraviolet radiation (UVR), often called black light, is one of many kinds of waves that are placed on the electromagnetic spectrum (see Figure A). All of the waves on the spectrum, including radio, microwave, infrared, visible light, ultraviolet, x-rays, and gamma rays, travel at the speed of light. Each type of radiation has a distinct relative intensity (see Figure B). Ultraviolet radiation is between visible light and x-rays on the spectrum. It consists of high-frequency wavelengths, invisible to the human eye, ranging from 200 nanometers to 400 nanometers. While the most common source of ultraviolet radiation is the sun, it is also utilized in hospitals, biological laboratories, and schools (World Health Organization, 1979). Ultraviolet radiation is used in photochemical processes, microscopy, photography, and irradiation of food and other products. Although research usually focuses on the harmful effects of ultraviolet light, there are many beneficial effects of UVR, as well. Certain benefits include "blood pressure gradually [falling] for twenty-four hours, and lowered pressure [persisting] for several days" (World Health Organization, 1979). The harmful effects of ultraviolet light outweigh the positive outcomes, though. Health risks arise from chronic and excessive exposure to UVR. It damages the skin, which can be seen in a sunburn or a tan (see Figure C). The affect of ultraviolet rays greatly depends on the season, time of day, latitude, and cloud cover (World Health Organization, 1979). Accumulated exposure to the sun can cause skin cancer. UV light also increases the risk of cataracts and other eye problems, and can subdue the immune system (Strange, 1995). Not all ultraviolet radiation behaves the same way. There is a great difference between longer-wavelength UVR and shorter-wavelength UVR. While longer-wavelength rays cause tanning, shorter-wavelength UVR causes sunburn and skin cancer (Hazen, 1996). As a result of these considerable differences among ultraviolet light, UVR is divided into the following three bands: UVA (320 to 400 nm), UVB (290 to 320 nm), and UVC (200 to 290 nm). In order to understand the effects of ultraviolet light, each band must be examined separately (see Figure D).
    Ultraviolet A radiation, stretching from 320 to 400 nanometers, is placed just beyond the violet portion of the visible spectrum. Short wavelength UVA is more damaging than long wavelength UVA. Although not much is known about the effects of Ultraviolet A radiation, it is know that, in general, UVA rays cause the skin to tan. Most researchers believe that UVA rays multiply the harmful effects of UVB radiation or accelerate the growth of existing cancer cells. UVA prematurely wrinkles and withers the skin, giving it an aged look (Brink, 1996). Although the other two types of ultraviolet radiation cannot, UVA radiation can penetrate window glass. The link between UVA light and skin cancer is currently being explored.
    Ultraviolet B radiation, existing from 290 to 320 nanometers, is more damaging than UVA, alone causing more than ninety percent of skin cancers including melanomas, the most deadly of skin cancers (Trichopoulos, 1996). UVB is located on the lower edge of ozone’s ultraviolet absorption band, also known as the "Huggins bands," and is responsible for most sunburns. Scattering plays a significant role in the damaging effects of UVB radiation, increasing the intensity of sunlight. Scattering is greatest for the shorter ultraviolet wavelengths; therefore, UVB is subject to the most atmospheric scattering (Giese, 1976). Ultraviolet B radiation is strongest at low latitudes and high altitudes. At higher latitudes, the sun is low in the sky and, therefore, it takes a longer path through the atmosphere and more of the UVB is absorbed (Parson, 1996). Although UVB rays are of very low intensity compared to UVA radiation, Ultraviolet B is the most dangerous and detrimental to living things, and more specifically to human beings. While most living things are protected from UVB radiation by feathers and fur, human beings do not have this natural form of defense. The best form of defense against UVB radiation is sunscreen, measured in terms of sun protection factor (SPF). For instance, a sunscreen of fifteen confers fifteen times more protection against UVB rays than using no sunscreen at all. Although sunscreens are protective against UVB radiation, studies have not yet proven that they block UVA rays well (Wentzell, 1996). A major concern of researchers is the depletion of the ozone layer, resulting in increased UVB radiation reaching the Earth. Currently, many UVB rays are prevented from reaching the Earth, but depletion of the ozone layer would only make humans more susceptible to burning and cancer. In fact, "the ozone layer has thinned by six percent to seven percent in the mid-latitudes of the Northern Hemisphere, which includes the United States, since 1979" (Brink, 1996). This increase allows six to fourteen percent more UVB rays through the Earth’s surface. UVB is the one type of ultraviolet radiation with which we, as humans, must be most concerned.
    Ultraviolet C radiation, reaching from 200 to 290 nanometers, does not reach the us; it is absorbed by the ozone layer (Marwick, 1995). It is a misconception that ozone is found at the Earth’s surface, though. Only nitrogen, oxygen, carbon dioxide, argon, neon, helium, krypton, xenon, hydrogen, methane, and nitrious oxide exist there. Despite this statement, research has shown that at higher levels of the atmosphere, between fifteen and thirty-five kilometers, above the Earth’s surface, ozone is found (Giese, 1976). The existence of oxygen on the Earth’s surface is the reason an ozone layer exists. Without the ozone layer and its absorption of UVC light, life on Earth would not be possible.
    In order to understand the existence of the ozone layer, the history of the atmosphere must be examined. Although we take our atmosphere for granted, it is important to note that atmospheres exists only if there is a gravitational field capable of holding gases. The Earth’s atmosphere was not always like it is today. The original atmosphere of the Earth probably looked like that of the sun originally, containing large amounts of hydrogen, helium, neon, argon, krypton, and xenon. When the amount of those elements are compared to the amount of the same elements existing in today’s atmosphere, there is a difference by several orders of magnitude. Most of the light gases in the original atmosphere must have escaped the Earth, probably due to its weak gravitational field. The light gases that remain from the original atmosphere are continuously leaving the Earth by diffusion. It can be assumed that a secondary atmosphere came into existence once the surface of the Earth had cooled down. This atmosphere, thought to be anaerobic or lacking in oxygen, formed slowly from gases being released from volcanoes. The exact composition of this secondary atmosphere is the subject of much debate. While some geologists believe that the atmosphere consisted of methane, ammonia, hydrogen, and water vapor, others think that it was formed of carbon dioxide, carbon monoxide, hydrogen, nitrogen, and water vapor. What is most important, however, is whether water vapor and oxygen existed. It is agreed that water vapor existed while oxygen did not. The secondary atmosphere was a reducing atmosphere - one in which the oxygen combined with some of the gases to form new compounds. This atmosphere probably permitted much UVC radiation to reach the Earth. Geological evidence shows that the Earth was without life for a long time; this can seemingly be contributed to the devastating effects of UVC radiation. Life in its early stages must have existed only in shady waters to prohibit the intrusion of UVC rays; this life was anaerobic, as well, because the atmosphere lacked oxygen for aerobic existence. The development of phototrophs that used the sun’s energy to produce their own nutrients was an essential step in the process of evolution. Life first appeared during the Paleozoic time period and oxygen probably reached its present level during this era. The appearance of invertebrate types at this time prompts the idea that significant geological changes were occurring (Giese, 1976). While much of the study of the origin of ozone in the atmospheric layer is speculative, it is known that ozone is essential to life on Earth as we know it.
    Research has shown that there is a strong connection between ultraviolet radiation and the three kinds of skin cancer - basal cell carcinomas, squamous cell carcinomas, and melanomas. In the United States in 1990 there were 500,000 cases of the first, 100,000 of the second, and 27,600 of the third (Parson, 1996). Although sun damage cannot be undone, there are ways to prevent oneself from inducing cancer. Sunscreens, protective clothing, and low-fat diets are a few preventative methods; staying out of the sun is the wisest idea, though. Dark skinned people are less likely to get skin cancer than those that are fair skinned (see Figure E). People who live in very sunny and warm places, such as Tucson, have an even greater chance of skin cancer. Early warning signs are unusual moles - ones that are raised, strangely shaped, or seem to grow in size.
    With an increasing number of people being diagnosed with skin cancer, much has been done to inform the public of the dangers of ultraviolet radiation. The National Weather Service provides the UV Index, which measures the ultraviolet exposure on a daily basis. The UV Index ranges from 0 to 10+ and indicates the amount of ultraviolet radiation reaching the Earth’s surface at noon. The index works as follows: from 0 to 2, the exposure level is minimal, 3 to 4 is low, 5 to 6 is moderate, 7 to 8 is high, and 9 to 10+ is very high (Strange, 1995). The United States government has also formed the National Cancer Institute for cancer research and information. The American Cancer Society is another association devoted to cancer research. Skin cancer and its causes are constantly under investigation; additional information is discovered on a regular basis.
    Although skin cancer is the most recognized detriment of ultraviolet light, cataracts are another impairment resulting from the sun. The evidence that links cataracts and ultraviolet light, particularly UVB rays, "is indirect, [but] very plausible" (Parson, 1996). What is definitely known is that too much ultraviolet exposure results in short-term "snow blindness" (Parson, 1996). All eyes, regardless of skin color genes, are vulnerable to sun damage. Cataracts are "a clouding of the lens that results in one million surgeries annually to substitute an artificial lens for a damaged one" (Brink, 1996). A 1988 study of Chesapeake Bay fisherman aged thirty to ninety-four showed that those who wore no eye protection since the age of sixteen had three times as many cataracts as those who wore sunglasses or a brimmed hat (Brink, 1996). Besides skin protection, we must all wear eye protection when in the sun to prevent cataracts.
    It is comforting to know that so much research is being done on skin cancer. Even with the current research, we still need to realize the harmful effects of ultraviolet radiation, particularly UVB light, and be cautious of its consequences. It is wise to remember that not only does ultraviolet light cause skin cancer, but that it also plays a significant role in the induction of cataracts. By being more knowledgeable on the damage inflicted by the sun and its ultraviolet rays, we can perhaps, in due time, lower the number of people diagnosed with skin cancer and cataracts. We can all help prevent the depletion of the ozone layer and the enhanced probability of ultraviolet light reaching the Earth’s surface. The American engineer C.F. Kettering said the following in the early 1900s: "We should all be concerned about the future because we will have to spend the rest of our lives there." I believe this is a worthy and exemplary creed to live by. Protect yourself when in the sun! Don’t be one of the 38,300 people that will be diagnosed with melanoma of the skin, the most deadly of skin cancers, this year (Editors of Scientific American, 1996).


List of References

Brink, Susan. "Sun Struck." U.S. News 24 June 1996. U.S. News Online. Online.        Netscape. 5 Nov. 1996.

Giese, Arthur C. Living with Our Sun’s Ultraviolet Rays. New York: Plenum Press,     1976.

Hazen, Robert M., and James Trefil. The Physical Sciences: An Integrated     Approach. New York: John Wiley & Sons, Inc., 1996.

Marwick, Charles. "New light on skin cancer mechanisms." Journal of the American     Medical Association 9 Aug. 1995. Expanded Academic ASAP. 5 Nov.     1996.

Parson, Robert. "The Effects of Ultraviolet Light." University of Oregon. Online.     Netscape. 5 Nov. 1996.

Strange, Carolyn J. FDA Consumer July-Aug. 1995. Expanded Academic ASAP. 5     Nov. 1996.

Trichopoulos, Dimitrios, Frederick P. Li, and David J. Hunter. "What Causes     Cancer?" Scientific American September 1996: 80-87.

"Twelve Major Cancers." Scientific American September 1996: 126-132.

Wentzell, J. Michael. "Sunscreens: the ounce of prevention." American Family     Physician April 1996. Expanded Academic ASAP. 5 Nov. 1996.

World Health Organization. United Nations Environment Programme, the World     Health Organization, and the International Radiation Protection Association.     Environmental Health Criteria: Ultraviolet Radiation. Geneva: World Health     Organization, 1979.

                                Courtney Ozer    
                                November 7th, 1996
                                NSc 105: Richardson
                                Term Paper

Outline

I.     Introduction Paragraph
A.     Overview of Cancer
B.     Focus on Skin Cancer
C.     Introduction to ultraviolet radiation and its effects

II.     Ultraviolet Radiation
A.     Its place on the electromagnetic spectrum
B.     What is the electromagnetic spectrum?
C.     What is ultraviolet radiation?
D.     Harmful/beneficial effects
E.     The difference between long-wavelength radiation and shorter-wavelength radiation.
F.     The division of UV rays into UV-A, UV-B, and UV-C

III.     Ultraviolet A Radiation
A.     Wavelength of UV-A radiation
B.     Difference between long wavelength UV-A and short wavelength UV-A
C.     Research on UV-A radiation
D.     Do sunscreens block this type of radiation?
E.     What UV-A does to the skin

IV.     Ultraviolet B Radiation
A.     Wavelength of UV-B radiation - the "Huggins bands"
B.     Research on UV-B radiation
C.     What UV-B does to the skin
D.     UV-B is more damaging than UV-A - causes 90% of skin cancer cases
E.     How animals protect themselves from UV-B radiation
F.     How SPF and window panes protects against UV-B radiation
G.     How depletion of the ozone layer would effect UV-B radiation

V.     Ultraviolet C Radiation
A.     Wavelength of UV-C radiation
B.     Research on UV-C radiation
C.     How the atmosphere absorbs UV-C from reaching us
D.     No life on earth if the ozone layer did not absorb UV-C

VI.     How Ultraviolet Radiation Causes Skin Cancer
A.     The different kinds of skin cancer
B.     Prevention techniques for skin cancer
C.     Certain populations that are at a greater risk for the disease
D.     Early warning signs
E.     The two step process of developing skin cancer
F.     Additional problems from ultraviolet radiation

VII.     What Has Been Done to Inform the Public of Ultraviolet Radiation?
A.     UV Index
B.     National Cancer Institute and American Cancer Society
C.     Continuous research on skin cancer

VIII.     Conclusion



Introduction

    According to the National Cancer Institute, cancer is now the second leading cause of death in the United States. It is slowly catching up to heart disease, the leading cause of death currently. With nearly one million cases of skin cancer expected in the United States this year, it has become the most common kind of cancer. The prevalence of skin cancer has prompted much research on the cause and possible prevention of the disease. Ultraviolet radiation has been found as the primary cause of skin cancer. Although there are beneficial effects from ultraviolet light as well, the main focus of research has been on its harmful effects. There are three kinds of ultraviolet radiation - Ultraviolet A, Ultraviolet B, and Ultraviolet C. Research has now shown how ultraviolet light penetrates the ozone layer and its effects on our skin. The purpose of this paper is to inform all of its readers of the harmful effects of sunbathing and neglecting to use sunscreen. Hopefully, it will cause people to be careful when in the sun. Ultraviolet radiation is damaging and must be studied in order to reduce the number of people that acquire skin cancer.