What is melanoma skin cancer?

Melanoma skin cancer is when abnormal cells in the skin start to grow and divide in an uncontrolled way. It starts in skin cells called melanocytes.

There are 2 main categories of skin cancer: 

• non melanoma skin cancer - including basal cell skin cancer, squamous cell skin cancer and other rare types
• melanoma skin cancer

This page is about melanoma skin cancer.

The skin

The skin is a body organ. It does several jobs, including:

• protecting the inside of the body from damage
• helping to keep our body temperature about the same
• getting rid of some waste products through sweat
• making vitamin D (this helps form and maintain our bones)

The skin is made up of 2 main layers, the epidermis and the dermis.

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.

Where melanoma skin cancer starts

Melanoma skin cancer can start anywhere on the skin. It may start:

• in a mole
• on a patch of normal skin
• on the palms of the hands or soles of the feet
• under the nails

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 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.

In people with white skin, melanoma is more common on skin that has been exposed to the sun. But it can start anywhere.

It’s melanin that gives you a sun tan. Melanocytes make more melanin when they are exposed to the sun. This is then transferred to other skin cells to protect them against the sun's rays.

People with brown or black skin do not have more melanocyte cells than people with white skin. But their melanocytes are more active and make more of the pigment.

Rarely melanoma can develop in areas not exposed to the sun. Melanomas in the palms of the hands, soles of the feet and under the nails are normally a type of melanoma called acral melanomas. They are not related to exposure to the sun. Acral melanomas are more commonly diagnosed in people with brown or black skin.

Who gets melanoma skin cancer?

Melanoma skin cancer can happen at any age, but it's more common in older people. Unlike most other cancer types, it's also quite common in younger people. 

Ultraviolet radiation from the sun or sunbeds is the main environmental factor that increases the risk of getting melanoma skin cancer.

Other risk factors include:

• skin type
• hair and eye colour
• number of moles
• family history of melanoma

How common is melanoma skin cancer?

Around 16,700 people are diagnosed with melanoma skin cancer in the UK each year. The number of people diagnosed has increased over the last few decades.

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