Sun and skin – a dangerous combination
Glossary
cancer. One of the defining features of most cancer cells is that they grow when they should not. Ignoring signals from the rest of the body, they tend to multiply regardless, encouraging blood vessels to supply them with food and oxygen at the expense of normal tissue nearby. Once a mass of cancer cells (a tumour) has grown large enough, it will often invade other tissues. It will eventually push through the wall of a lymph vessel or blood vessel and clumps of cancer cells will break off and travel around the body. The cancer can then be very hard to cure. The clumps (called metastases) can settle almost anywhere and start to grow as a tumour. The whole body is soon seeded with tumours of the original cancer cell type. Usually, it is then only a matter of time before vital functions are interfered with and the patient dies.
cataracts. Cloudiness in the lens of the eye, or the covering capsule of the lens, dimming the eyesight, producing distorted images, and eventually causing blindness. Cataracts can have several causes, one of which is prolonged exposure to too much sunlight.
DNA (deoxyribonucleic acid). The nucleic acid forming the genetic material of all organisms with the exception of some viruses which have RNA. DNA is present in the nucleus and other organelles such as mitochondria and chloroplasts.
electromagnetic radiation. Electromagnetic radiation is simply energy which travels through space at about 300,000 kilometres per second – the speed of light. We imagine radiation moving like a wave. The distance between two adjacent wave crests is called a wavelength. The shorter the wavelength, the more energetic the radiation is said to be. Also, the shorter the wavelength, the greater the frequency of the radiation. Other than wavelength, frequency and energy there is no difference between a radio wave, an X-ray and the colour green. They all possess the same physical nature. For more information see Back to Basics: Electromagnetic radiation (Australian Academy of Science) and Electromagnetic Spectrum (NASA's Observatorium, USA).
gene. The basic unit of inheritance. A gene is a segment of DNA that specifies the structure of a protein or an RNA molecule.
melanin. A dark pigment produced by cells called melanocytes in the skin. It absorbs ultraviolet radiation and is thus a natural sunscreen. Exposure to ultraviolet radiation stimulates more melanin production, resulting in a tan. However, getting a tan entails the risk of skin damage. Dark-skinned people naturally produce much more melanin than fair-skinned types and so are less liable to experience sunburn or skin cancer.
moles. Areas of pigmentation, darker than the surrounding skin, and often raised. Harmless moles are usually less than about 5 millimetres across and have well-defined edges. A change to a mole or the appearance of a new one could indicate cancer. The number of moles on a person seems to be an indication of their exposure to the sun.
mutagen. Any agent (such as a chemical substance or radiation) that induces mutations by permanently altering the genes or chromosomes.
ozone. Ozone (O3) is a form of oxygen. It is a colourless gas that has a very pungent odour. It exists naturally at low concentrations in the stratosphere where it absorbs ultraviolet radiation. In the troposphere it exists naturally at extremely low concentrations. But these concentrations increase when sunlight acts on various gases, coming mainly from vehicle exhausts, and ozone then becomes a pollutant in the troposphere. Ozone is a highly corrosive gas and is poisonous to most organisms. At concentrations as low as 0.00001 per cent (or 10 parts per hundred million) it can irritate the membranes lining the nose, throat and airways and can trigger or exacerbate asthma attacks.
pterygium. A small non-cancerous growth in the eye, arising from the outer layer of the eyeball. It is associated with long-term exposure to sunlight. Most pterygia are easily removed.
solar keratoses. (Also known as sunspots.) These are harmless areas of slightly changed pigmentation, not as distinct as freckles or moles. Although not cancerous, they are a sign of skin damage by ultraviolet radiation. Actinic keratoses are more scaly growths which may develop into cancer.
ultraviolet (UV). A form of electromagnetic radiation. Ultraviolet radiation has shorter wavelengths than visible light and is therefore carries more energy. It is divided into three broad categories: A, B and C. UV-A has the longest wavelength and is the least damaging form, although sufficient exposure will cause sunburn. UV-B damages proteins in unprotected organisms and can cause cancer, while UV-C is extremely dangerous because it can cause mutations in DNA.
Posted March 1997.