Ultraviolet Radiation and Human Health
You marvel at the beauty of a butterfly’s wings. To you the pattern of the left wing is identical to the wing on the right. But what you see is not what you get – seen under ultraviolet light, the pattern of each wing is very different. If you had the facetted eyes of a butterfly you too could see light with shorter wavelengths than that of violet light (400nm). You would see the world with different eyes – metaphorically and literally.
UV light radiates at wavelengths between 100 and 400nm. Whereas visible light is broken up into its primary colours of red, green and blue and many shades, UV light has less fancy names for its subdivision: UVA, UVB, and UVC.
Ultraviolet light Visible light
Colour UVC UVB UVA Violet Blue Cyan Green Yellow Orange Red
Wavelength (nm) 100-280 280-320 320-400 400 450 500 550 580 600 700
UVC has the shortest wavelengths. It is absorbed by the atmosphere and doesn’t reach the earth’s surface. The amount of UVB radiation reaching the ground depends largely on the state of the ozone layer in the upper atmosphere, which we all know is thinning. Record levels of UVB radiation have been recorded in parts of Europe, North America and Australasia. UVA, on the other hand, radiates at longer wavelengths and reaches the earth’s surface almost unhindered, as it is not absorbed by the ozone layer.
While the sun is the major source of UV radiation, some man-made sources also produce high levels of UV light. Tanning devices, such as sun beds and sun lamps, emit mostly UVA, but some radiate UVB as well. The processes of arc welding and sterilization of medical equipment produce UV radiation. The white light of quartz halogen lamps is becoming increasingly popular at work and at home, but unshielded globes expose you to harmful UV radiation, especially at close quarters.
How much radiation you will absorb depends on many factors:
- The angle at which the UV rays strike your body or the earth’s surface. Your body parts that are almost perpendicular to the angle of the rays receive most radiation. The shoulders and the nose burn first while you stand and, of course, most of the body is at risk while you lie on the beach. Around noon and in summer, when the sun is high in the sky, you are likely to receive the highest dose. The angle of radiation also depends on the geographical latitude. The sun’s rays strike the earth’s surface more directly the closer you are to the equator.
- Ground reflection. Most surfaces reflect only a small amount of UV radiation. The sand at the beach, however, reflects around 25% and fresh snow almost 80%. You can add these figures to the amount of radiation you receive directly from the sun.
- Altitude. When you are exposed to fresh snow you are probably in the mountains. With or without snow, the closer you are to the sun the higher the intensity of UV radiation. Because the earth’s atmosphere rapidly thins out with altitude and the mountain air usually contains less pollution, fewer molecules are available to absorb UV radiation. For every 300m the level increases by approximately 4%.
- Particles in the atmosphere. The most obvious particles are water droplets in the form of clouds – we all know how a blanket of cloud keeps a significant amount of sunlight from reaching the ground. Unfortunately, clouds don’t affect UV light very much. A thin layer makes hardly any difference to the radiation level and even a thick layer can reduce it by less than 10%. Only dark storm clouds will shield you from UV radiation. If there is one good thing about pollution, it does absorb some of the UV radiation. How much is still a matter of research. On the other hand, pollution particles also scatter radiation into shady spots.
- Water. UV radiation penetrates the water. Almost all reaches to just below the surface and up to 40% penetrates to a depth of 0.5 meter
UV Radiation and Health
One important and probably only beneficial effect of UV radiation on your health is the formation of vitamin D3 in your skin. The body requires this vitamin to help with the absorption of calcium and phosphorus. If you would be without sunlight for a long time, your bones would become soft and deformed, a disease known as rickets. But as latest studies suggest, exposure of your hands and face for as little as 15 minutes per day should be sufficient to prevent the disease.
If you expose your eyes, skin and immune system to the sun, a photochemical reaction in proteins and your DNA occurs. Too much exposure to UV radiation temporarily or permanently alters the function of cell components.
In the short term, tiny blood vessels can burst and redden the skin or the eyes. Sunburn of the skin and inflammation of the eye (e.g., snow blindness) may follow. While these effects are reversible, further exposure can lead to permanent damage, such as the clouding of eye lenses, otherwise known as cataracts. The otherwise elastic fibres of your skin thicken due to a loss of collagen and your skin ages prematurely. UV radiation can even change the genetic information stored within your DNA and may initiate cancer to the skin or the eyes. UV radiation also suppresses the immune system’s ability to fight intruders such as viruses, bacteria and parasites.