Skin cancer is the uncontrolled growth of abnormal cells in the skin.
The three main types of skin cancer are basal cell carcinoma (BCC), squamous cell carcinoma (SCC) and melanoma. BCC and SCC are also called non-melanoma skin cancer or keratinocyte cancer. They are far more common than melanoma.
Rare types of non-melanoma skin cancer include Merkel cell carcinoma and angiosarcoma. They are treated differently from BCC and SCC.
The skin
The skin is the largest organ of the body. It acts as a barrier to protect the body from injury, control body temperature and prevent loss of body fluids. The two main layers of the skin are the epidermis and dermis.
The epidermis is the top, outer layer of the skin. It contains three main types of cells:
- squamous cells – these flat cells are packed tightly together to make up the top layer of skin. They form the thickest layer of the epidermis.
- basal cells – these block-like cells make up the lower layer of the epidermis. The body makes new basal cells all the time. As they age, they move up into the epidermis and flatten out to form squamous cells. The basal cells sit on a very thin layer of tissue (the basement membrane) that separates the epidermis from the rest of the body.
- melanocytes – these cells sit between the basal cells and produce a dark pigment called melanin that gives skin its colour. When skin is exposed to ultraviolet (UV) radiation, melanocytes make melanin to try to protect the skin from getting burnt. Melanocytes are also found in non-cancerous spots on the skin called moles or naevi.
The dermis layer of the skin sits below the epidermis. It is made up of fibrous tissue and contains the roots of hairs (follicles), sweat glands, blood vessels, lymph vessels and nerves. All of these are held in place by collagen and elastin, the proteins that give skin its strength and elasticity.
Your guide to best cancer care
A lot can happen in a hurry when you’re diagnosed with cancer. The guide to best cancer care for basal and squamous cell carcinoma can help you make sense of what should happen. It will help you with what questions to ask your health professionals to make sure you receive the best care at every step.
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Basal cell carcinoma (BCC)
BCC is the most common type (about 66% of skin cancers) and starts in the basal cells of the skin. BCC usually grows slowly over months or years and only rarely spreads to other parts of the body. If left untreated, some BCCs can grow deeper into the skin, invade nerves and damage nearby tissue, making treatment more difficult.
Having one BCC increases the risk of getting another, and there can be more than one BCC at the same time on different parts of the body.
Signs of BCC
- Develops on areas that get more sun exposure, such as the head, face, neck, shoulders, lower arms and legs, but can occur anywhere on the body.
- May appear as a pearl-coloured lump or slightly scaly area that is shiny and pale or bright pink, or some may appear darker.
- The skin may break down (ulcerate), bleed and become inflamed. It may appear to heal and then become inflamed again.
Squamous cell carcinoma (SCC)
SCC is the second most common type (about 33% of skin cancers) and starts in the squamous cells of the skin. SCCs can grow quickly over several weeks or months.
Some are found only in the top layer of the skin. These are called SCC in situ, intra-epidermal carcinoma or Bowen’s disease. If SCC invades through the basement membrane it is called invasive SCC. If left untreated, this can spread to other parts of the body (metastatic SCC). SCC on the lips and ears is more likely to spread.
Signs of SCC
- Usually appears on parts of the body most often exposed to the sun, such as the head, neck, hands, forearms and lower legs, but can start anywhere.
- Often appears as a thickened, red, scaly or crusted spot or rapidly growing lump.
- May bleed and become inflamed, and is often tender to touch.
Other skin spots
Some spots that appear on the skin are not cancerous. If you are concerned about any mark or growth on your skin, see your general practitioner (GP).
Sunspots (actinic or solar keratoses)
Sunspots occur more often in people over 40, but anyone can develop them. They usually appear on skin that’s frequently exposed to the sun, such as the head, neck, hands, forearms and legs. Sunspots are a warning sign that the skin has had too much sun exposure. Very rarely sunspots may develop into SCC.
Signs of sunspots include:
- flat, scaly spot that feels rough and are often the colour of your skin or red
- can be easily scratched off but will return in a few days
- may develop into skin cancer.
Moles (naevi)
A mole (naevus) is a normal skin growth that develops when melanocytes grow in groups. Moles are very common. Some people have many moles on their body – this can run in families. Overexposure to the sun, especially in childhood, can also increase the number of moles. People with large numbers of normal moles can have a higher risk of melanoma.
Signs of moles include:
- brown, black or the same colour as your skin
- usually round or oval
- are harmless.
Dysplastic naevi
People with many irregular moles (dysplastic naevi) have a greater risk of developing melanoma. This risk increases with the number of moles that a person has.
Signs of dysplastic naevi include:
- mole with an irregular shape and uneven colour
- may develop into skin cancer.
Age spots (seborrhoeic keratoses)
These very common skin growths can occur anywhere except the palms and soles. They may look similar to a skin cancer or sunspot. They may be itchy and may bleed if scratched.
Signs of age spots include:
- raised warty area on the skin that feels rough
- light to very dark brown in colour
- are harmless.
Causes
Over 95% of skin cancers are caused by exposure to UV radiation. When unprotected skin is exposed to UV radiation, how the cells look and behave can change.
UV radiation most often comes from the sun, but it can also come from artificial sources, such as arc welders, glue curing lights (e.g. for artificial nails) and solariums (also known as tanning beds or sun lamps). Solariums are now banned for commercial use in Australia because research shows that people who use solariums have a much greater risk of developing skin cancer.
Most parts of Australia have high levels of UV radiation from the sun all year round. UV radiation cannot be seen or felt and it is not related to temperature. It can cause sunburn, premature skin ageing and damage to skin cells, which can lead to skin cancer. You can’t always see sun damage to the skin – it can start long before you get sunburnt or develop a tan, and the damage adds up over time.
Risk factors
Anyone can develop skin cancer but it’s more common as you age. Many factors can increase your risk, including having:
- pale or freckled skin, especially if it burns easily and doesn’t tan
- red or fair hair and light-coloured eyes (blue or green)
- unprotected exposure to UV radiation, particularly a pattern of short, intense periods of sun exposure and sunburn, such as on weekends and holidays
- actively tanned or used solariums
- worked outdoors or been exposed to arsenic
- a weakened immune system – this may be from having leukaemia or lymphoma or using immunosuppressive medicines (e.g. for rheumatoid arthritis, another autoimmune disease or for an organ transplant)
- lots of moles, or moles with an irregular shape and uneven colour
- a previous skin cancer or a family history of skin cancer
- certain skin conditions such as sunspots.
People with olive or very dark skin have more protection against UV radiation because their skin produces more melanin than fair skin does. However, they can still develop skin cancer.
How common is skin cancer?
Australia has one of the highest rates of skin cancer in the world. About two in three Australians will be diagnosed with some form of skin cancer before the age of 70.
Non-melanoma skin cancer is the most common cancer diagnosed in Australia. Over one million treatments are given each year in Australia for non-melanoma skin cancers. BCC can develop in young people, but it is more common in people over 40. SCC occurs mostly in people over 50.
Understanding Skin Cancer
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Expert content reviewers:
A/Prof Stephen Shumack, Dermatologist, Royal North Shore Hospital and The University of Sydney, NSW; Dr Margaret Chua, Radiation Oncologist, Head of Radiation Oncology, Skin and Melanoma, Peter MacCallum Cancer Centre, VIC; John Clements, Consumer; Aoife Conway, Skin Lead and Radiation Oncology Nurse, GenesisCare, Mater Hospital, NSW; Sandra Donaldson, 13 11 20 Consultant, Cancer Council WA; Kath Lockier, Consumer; Dr Isabel Gonzalez Matheus, Plastic and Reconstructive Surgery, Principal House Officer, Princess Alexandra Hospital, QLD; A/Prof Andrew Miller, Dermatologist, Canberra Hospital, ACT; Dr Helena Rosengren, Chair Research Committee, Skin Cancer College of Australasia, and Medical Director, Skin Repair Skin Cancer Clinic, QLD; Dr Michael Wagels, Staff Specialist Plastic and Reconstructive Surgeon, Princess Alexandra Hospital and Surgical Treatment and Rehabilitation Service, and Senior Lecturer, The University of Queensland, QLD; David Woods, Consumer.
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The information on this webpage was adapted from Understanding Skin Cancer - A guide for people with cancer, their families and friends (2021 edition). This webpage was last updated in March 2022.