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  • Research shows a clear link between UV and skin cancer.

    The skin of an average adult has a total surface of about 1.8 square metres and a total weight of about 11 kilograms. This makes our skin our largest organ – and certainly an organ that we should look after!

    Rights: Nick Towers

    Human skin

    An illustration by Nick Towers, a children's book illustrator, showing the skin of a human head.

    Skin has several important functions including acting like a shield to protect our body from:

    • physical impact such as pressure and blows
    • temperature impact such as heat or cold
    • environmental impact such as the Sun’s UV radiation, bacteria and chemicals.

    Moles and melanoma

    Hayley Reynolds and Associate Professor Rod Dunbar explain the changes in moles that can be signs of melanoma developing.

    UV and melanoma

    Dr Elizabeth Baird, discusses melanoma and the damaging role of UV (UVA and UVB) on the skin.

    Skin cancer (carcinoma) is the uncontrolled division and growth of abnormal skin cells. Your skin has two main layers and several kinds of cells. The top, or outer, layer of your skin is called the epidermis. Skin cancers are classified by the type of epidermal skin cells that become cancerous.

    Rights: The University of Waikato Te Whare Wānanga o Waikato

    Cross section of skin

    Diagram showing a cross section of skin on the left and on the right a cross section showing the cell types.

    Nature of Science

    Scientists often use diagrams that are labelled to communicate detailed information. Scientists in a particular area will have a common understanding of these diagrams and the scientific language used.

    Types of skin cancer

    There are three common types of skin cancer:

    • Basal cell carcinoma develops from abnormal growth of the basal cells – the round cells in the lowest layer of the epidermis.
    • Squamous cell carcinoma develops in the flat scaly cells called squamous cells – found in the middle of the epidermis.
    • Malignant melanoma occurs in the cells called melanocytes – responsible for producing the pigment melanin, which gives your skin its colour.
    Rights: Public domain


    Image of a typical melanoma showing colour differences.

    Which is the worst kind of skin cancer?

    • Basal cell carcinoma is the most common and the least dangerous skin cancer. If it isn’t removed, it will be disfiguring, but it is not likely to metastasise (spread to other parts of the body).
    • Squamous cell carcinoma is easily treated if it is found early enough but can be fatal if left untreated. Melanoma is the least common but the most deadly form of cancer.
    • Melanoma does metastasise and spread to other organs, where it can grow rapidly and affect the ability of that organ to function properly. There is no effective treatment for melanoma that has metastasised to distant organs. It is generally incurable.

    What is melanoma?

    Dr Elizabeth Baird outlines what melanoma is. She explains what is meant by dissemination and why it is so important to remove melanoma before it disseminates.

    What causes skin cancer?

    Research has shown that these skin cancers generally develop because of over-exposure to UV radiation (from the Sun or from sunlamps or tanning beds). Each time your unprotected skin is exposed to UV, the UV causes changes to take place in the structure of the genes and in the behaviour of the cells.

    Risk factors for melanoma

    Dr Elizabeth Baird, outlines the relationship between UV, melanocytes in the skin, tanning and melanoma risk. She discusses the risk factors of skin type and family history in the development of melanoma.

    Normally, cells grow and multiply in an orderly way. However, damaged genes can cause cells to behave abnormally. These abnormal cells may grow into a lump (a tumour). These tumours will either be benign (not cancerous) or malignant (cancerous). Benign tumours can grow, but they do not spread to other parts of the body (metastasise).

    Skin cancer statistics in New Zealand

    Dr Elizabeth Baird gives information on the risks of melanoma and other skin cancers in New Zealand compared with elsewhere.

    At first, a malignant tumour will stay confined to its original site. (This is called carcinoma in situ.) However, if the cells are not treated quickly, they may spread into surrounding tissue and to other parts of the body. (This is called malignant or invasive cancer.) When these cancer cells reach another part of the body, they may continue to grow and form another tumour. This is called a secondary cancer (or a metastasis).

    How is skin cancer treated?

    Diagnosing melanoma

    Dr Elizabeth Baird outlines the procedure used to diagnose and remove a melanoma.

    Different types of cancer require different kinds of treatment. These include:

    • surgical removal (the most common treatment)
    • chemotherapy
    • radiation therapy
    • immunotherapy
    • hormone therapy.

    What is lymphoscinitigraphy?

    Associate Professor Rod Dunbar (University of Auckland) explains the procedure of lymphoscintigraphy as a technique to determine the first lymph nodes melanoma will spread to.

    Once a cancer has developed, the outlook depends on a number of factors, including the type of cancer and how quickly it is diagnosed and treated.

    Related content

    These related articles explain why New Zealand skin cancer rates are so high, some of the risk factors and how skin cancer is diagnosed and treated.

    Activity idea

    For those interested in protection from UV, see The face of melanoma – an activity that looks at lifestyle factors that contribute to skin cancer.

    Useful links

    The SunSmart website is designed for students, teachers, schools and parents. It has information about UV, shade, hats, sunscreen, skin cancer and sun protection, as well as cross-curricula resources for teachers in the SunSmart Schools section.

    The Cancer Society of New Zealand is the leading organisation dedicated to reducing the incidence of cancer and ensuring the best cancer care for everyone in New Zealand.

    Melanoma New Zealand is a charity dedicated to preventing avoidable deaths and suffering from melanoma.

    This Skin Cancer Foundation web page looks at skin types and at risk groups.

    This HealthMatch article, Top 20 skin cancer hot spots in the world and why they're on the list, explores the roles that personal, cultural, and global habits play in rates of skin cancer and what we can do to change them.

      Published 29 July 2008, Updated 13 October 2021 Referencing Hub articles
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