![]() Due to their long half-lives (lasting between 50–100 years), the long-term damage they can cause to ozone is quite extensive. They were commonly found in solvents, aerosol sprays and coolants in refrigerators. The emission of chloroflourocarbons (CFCs) massively increases the concentration of these free radicals which then leads to the depletion of the ozone layer.ĬFCs are compounds made from carbon, fluorine and chlorine, which were invented in the 1920s. ![]() Free radicals such as chlorine and bromine atoms shift the cycle to produce more O 2 than O 3 this depletes the ozone layer. It is continually being regenerated from O 2 through the UV dependent ozone-oxygen cycle. Ozone is a triatomic oxygen molecule, O 3, found mainly in the stratosphere, which is approximately 10–40 km above the Earth's surface. The Earth receives UVR from the sun, all of the UV-C and the majority of UV-A and UV-B is filtered out by the ozone layer. 8 Although UV-B appears to be more important than UV-A as a risk factor, a causal link to UV-A exposure is also supported by data from patients using tanning beds 9 and or treated with psoralan UV-A (PUVA) for psoriasis. This is supported by the higher incidence of melanoma in equatorial regions than in latitudes further from the equator, as UV-B radiation is most intense at the equator while UV-A intensity varies less across latitudes. UV-B appears more closely associated with the development of melanoma than UV-A (320–400 nm). Exposure to UVR, fair skin, dysplastic naevi syndrome and a family history of melanoma are major risk factors for melanoma development. 7 Melanoma is also the third most common cancer among 15–39 year olds. An American study revealed that an increase in skin biopsy rates corresponded to an increase in the incidence of local melanoma while mortality rates remained unchanged, the authors have attributed the rising incidence of melanoma to an increase in diagnostic scrutiny rather than an actual increase in the incidence of disease. This is likely to be due to increased UV exposure, however the number of skin biopsies now taking place has also risen. Over the last 25 years the reported incidence of malignant melanoma has increased. Malignant melanoma is the most serious form of skin cancer: it is responsible for around 80% of skin cancer deaths. 5 They are found almost exclusively on sun-exposed skin such as the neck, face and arms, and the incidence is linked with geographical location, being higher at latitudesreceiving more sun such as Australia. SCCs are caused by sunlight-induced mutations in the p53 tumour suppressor gene. SCCs account for a significant proportion of non-melanocytic skin cancer. 3 The exact nature of the wavelengths and exposure patterns involved in BCC carcinogenesis is still equivocal to a large degree, however recent studies demonstrate a correlation between ultraviolet B radiation (UV-B, 290–320 nm) and BCC risk. An Italian study has also highlighted a definite association between BCC development and recreational sun exposure during childhood and adolescence. Patients with these malignancies are usually fair-skinned and tend to burn rather than tan in sunlight. Approximately 90% of skin cancers are non-melanocytic, the vast majority of these are BCCs.īCCs are commonly known as rodent ulcers they usually arise in sun-exposed areas of the body and have a propensity to cause extensive local tissue damage. Exposure to ultraviolet radiation is recognized as a risk factor in all three malignancies. The three most common types of skin cancer are basal cell carcinoma (BCC), squamous cell carcinoma (SCC) and malignant melanoma (MM). Any one of these effects of UVR may contribute to the induction of skin cancers by other agents such as viruses, X-rays or chemical carcinogens. 2 The immunosuppressive effect of UVR contributes to its carcinogenic activity. While UVB causes considerable DNA damage in the skin, UVA has only recently been shown to induce pyrimidine dimerizations and generate reactive oxygen and nitrogen species which damage DNA, proteins and lipids. Hence UV-C carries the most energy and is the most damaging to biological systems. 1 The wavelength of light is inversely proportional to its frequency and higher frequencies of light possess more energy. UV light can be further subdivided in terms of wavelength ‘long wave’ UV with a range of 320–400 nanometres (nm) is known as UV-A ‘medium wave’ UV with a range of 290–320 nm is known as UV-B and ‘short wave’ UV with a range of 100–290 nm is known as UV-C. The colour violet corresponds to the shortest wavelength in visible light and UV actually means ‘beyond violet’ (from the Latin ultra, meaning ‘beyond’). Ultraviolet radiation (UVR) occupies the space between visible light and X-rays on the electromagnetic spectrum.
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