Patient information from BMJ

Skin cancer (melanoma): what is it?

Last published:Jul 08, 2019

Melanoma is a type of skin cancer that usually starts within a mole or a dark spot on your skin. If you find it early before it spreads, a simple operation to remove it works well and usually leads to a cure.

Here, we look at how melanoma develops and its warning signs. To read about how doctors diagnose and treat melanoma, see our leaflet Skin cancer (melanoma): how is it diagnosed and treated?

What is melanoma?

Melanoma is a form of cancer that starts in skin cells called melanocytes. Melanocytes make the dark pigment called melanin that makes your skin darker when you’ve been in the sun.

It’s important to find a melanoma early on. If you don’t have a melanoma treated quickly, it could grow deeper into your skin and spread to other parts of your body.

Melanoma is the most serious type of skin cancer. It affects young people more often than older people. Older people are more likely to get a type of skin cancer called squamous cell cancer. To learn more, see our leaflet Skin cancer (squamous cell).

Doctors don’t know exactly what causes melanoma. But too much exposure to ultraviolet (UV) rays from the sun seems to trigger changes to melanocyte cells. These changes may make the cells grow in an abnormal way and turn cancerous. We don’t know why some moles turn cancerous while others don’t.

Some people are more likely than others to get melanoma. Having lots of moles (more than 50), especially ones with jagged edges, makes it more likely. Other things that increase your chance of getting this type of cancer include having relatives who have had melanoma, having had bad sunburn as a child, and having freckles, fair skin and hair, and blue or green eyes.

Going to tanning booths or using a sun lamp can also increase your risk, as this also exposes your skin to UV rays.

What are the warning signs?

The two main warning signs of melanoma are changes in a mole that you already have, or a new mole or dark spot appearing on your skin. See your doctor if you find a mole that has changed in shape, size or colour, or that feels different (rougher or scalier than before), hurts, itches, or bleeds.

There's an easy way to remember what to look for. Just think of ABCDE.

A stands for asymmetry. This means that the mole isn't round and even, like a circle. If you drew a line through the middle of the mole, the two sides would not match.

B stands for border. A normal mole has a smooth border. The moles you need to watch out for are the ones with jagged edges or notches in the edges.

C stands for colour. If your mole has different shades of colour, you should get it checked out. Possible colours include black, tan, red, blue, and white.

D stands for diameter, which is the distance from one side of the mole to the other. Look out for moles that are wider than a pencil eraser. But remember: the smaller a melanoma is when you find it, the better your chances of getting rid of it.

E stands for evolution. This means that the mole has changed - for example, its shape, size or colour has changed, or it feels different.