Ultraviolet radiation from the sun is known to cause damage to the skin. The most severe damage it causes is skin cancer. There are two main types of skin cancer caused by ultraviolet light: malignant melanoma and the more benign carcinoma.
Skin damage by the sun
Ultraviolet light from the sun can cause many changes to the skin, including a number which are associated with aging. These include texture changes, colour changes and changes to blood vessels. Ultraviolet light can also cause changes (mutations) in the DNA inside cells (Witkin, 1969), and this can eventually lead to skin cancer.
Ultraviolet rays cause mutations leading to skin cancer
Research by Daya-Grosjean et al (1995) confirms that an overwhelming majority of skin cancer cells contain mutations which have been caused by UV light. There are two categories of ultraviolet light which are believed to cause skin damage.
UVA is radiation with the longest wavelength, and accounts for most of the UV radiation arriving at the surface of the earth. It can penetrate the skin more deeply than UVB, and is implicated in premature aging. Until recently it was not believed to cause damage to cells, but it is now known to damage cells in the basal layer of the skin (Wishermann et al, 2008).
UVB radiation has a shorter wavelength and although it makes up a much smaller proportion of the light reaching the earth’s surface, it is much more damaging to cells. It only affects the outer layers of the skin since it cannot penetrate as far as UVA light, but it causes mutations much more readily, and is responsible for causing sunburn.
Put simply, sunburn is part of the body’s defense mechanisms against cancer. Mutations caused by UV light are detected by the cell, which triggers apoptosis (cell suicide). The cells with damaged DNA die, and this is why the skin “peels” after burning. Repeated sunburn can result in some cells having mutations in their apoptosis mechanisms, and this can lead to growth of the abnormal cells causing carcinoma.
Melanoma can also be caused by UV induced mutations, but it is not linked to repeated cases of sunburn.
Symptoms of malignant melanoma
Melanomas are most common on the back, legs, arms or face, but can appear anywhere on the body. Patients should consult their doctor if a new mole appears, or an existing mole changes shape. Melanomas are usually larger than normal moles, with a diameter greater than six millimeters (a quarter of an inch) and they may be raised above the surface of the skin. They may have an irregular shape and a border which is not clearly defined, and they often contain more than one colour.
Malignant melanoma treatments and prognosis
Treatment of melanoma depends on how advanced the disease has become when a diagnosis is made. Early cases can be treated simply by surgical removal of the melanoma, but in more advanced cases, local lymph nodes may also be removed under general anaesthetic, and injections of interferon may be given to help the body attack any remaining cancerous cells. The prognosis is poor for advanced stages of the disease, but chemotherapy and radiotherapy may be administered to slow down the advance of the cancer and prolong life.
Symptoms of carcinoma
There are two main types of non-melanoma skin cancer: the more common basal cell carcinoma, which affects the cells of the epidermis (beneath the surface of the skin), and squamous cell carcinoma, which affects cells at the surface of the skin.
Basal cell carcinoma usually appears as a waxy-looking whitish lump on the skin, or a flat patch of scaly-looking skin which may be flesh-coloured or brown. They are generally painless, but the patches can grow quite large: up to four to six inches in diameter.
Squamous cell carcinomas are firm red lumps, or scab-like lesions which do not heal. Both types of carcinoma are most commonly found on parts of the skin which are regularly exposed to sunlight.
Carcinoma treatments and prognosis
Prognosis for non-melanoma skin cancer is generally very good, as this type of cancer rarely spreads to other parts of the body. Treatment is usually by surgical excision, or removal of the tumour by another means such as cryotherapy or electrocautery. However, in cases where removal would cause disfigurement, radiotherapy may be used to kill the cancerous cells. Chemotherapy is not often used to treat non-melanoma skin cancer.
Sources:
E M Witkin “Ultraviolet-Induced Mutation and DNA Repair” Annual Review of Genetics 3, 525-552 (1969)
L Daya-Grosjean, N Dumaz, A Sarasin “The Specificity of p53 Mutation Spectra in Sunlight Induced Skin Cancers” Journal of Photochemistry and Photobiology B: Biology 28, 115-124 (1995)
K Wishermann, S Popp, S Moshir “UVA Radiation Causes DNA Strand Breaks, Chromosomal Aberrations and Tumorigenic Transformation in HaCaT Skin Keratinocytes” Oncogene 27, 4269-4280 (2008)
Skin Cancer Foundation “Understanding UVA and UVB”
Skinsight.com
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Veronica Mitchell - Veronica studied veterinary medicine at Cambridge University before becoming a secondary school science teacher. She enjoys writing about ...
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