What is skin cancer?

The Skin

The skin does several jobs including:

  • protecting the inside of the body from damage

  • helping to keep our body temperature more or less the same

  • getting rid of some body waste products through sweat

  • making vitamin D (this helps form and maintain our bones)

Diagram showing the structure of the skin

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The skin is made up of 2 main layers: the epidermis on the outside and the dermis beneath.

The thickness of the epidermis and the dermis varies depending on the part of the body the skin is covering. For example, the skin on the soles of your feet is quite thick, with an epidermis and dermis of about 5mm. The skin on your eyelids is much thinner, about 0.5mm.

Sun damage is the cause of most skin cancers. The cells in the epidermis are most at risk of sun damage.

The most common type of cells found in the epidermis are called keratinocytes. Basal cells are a type of keratinocyte found at the bottom of the epidermis. The basal layer is where all normal skin cells come from, and where basal cell cancer (BCC) develops.

Skin Cancer

Non melanoma skin cancer

Non melanoma skin cancer that includes basal cell skin cancer, squamous cell skin cancers and other rare types.

BCC is the most common type of skin cancer. It mostly develops in areas of skin exposed to the sun such as the head, face, ears and neck.

The top two layers of the skin are made up of cells that have died and pushed up from the basal layer. They're filled with keratin made from keratinocytes. It's a tough waxy substance that helps to make the skin strong to protect the body.

Squamous cell cancer (SCC) also develops from keratinocytes in the epidermis. These develop in the cell layer just above the basal layer.

Skin cancers can grow slowly and it can take some years before a cancer is noticed. But sometimes a skin cancer can grow very quickly, within a few months.

Around 147,000 cases of non melanoma skin cancer are diagnosed in the UK each year. The number could be higher as we know that they are under reported. This makes it the most common type of cancer by far. Because non melanoma skin cancers are easy to treat and cure, they're often left out of national cancer statistics.

Melanoma Skin Cancer

Melanoma starts in cells in the skin called melanocytes. These cells are in the deep layer of the epidermis between the layer of basal cells.

Melanocytes make a pigment called melanin. This gives skin its natural colour. The pigment helps to protect the body from ultraviolet light (UV radiation) from the sun.

UV radiation can cause sunburn. This is a sign of damage to the genetic material (DNA) in skin cells. Over time, enough DNA damage can cause cells to grow out of control and lead to cancer.

People who originally come from hotter climates with more sunshine tend to have naturally darker skins. They do not have more of the melanocyte cells than people with pale skin. But their melanocytes are more active and make more of the pigment.

In paler people, the pigment gives you a sun tan. Exposing your skin to the sun makes the melanocytes make more pigment. The pigment is then transferred to the other skin cells to protect them against the sun's rays.

Around 16,000 people are diagnosed with melanoma in the UK each year. Over the last 10 years, the number of people diagnosed with melanoma in the UK has increased by almost half.

Melanoma is the 5th most common cancer in the UK.

Web content: Cancer Research UK, Accessed Oct 2019.

Skin Cancer Risks & Causes