The first sign of a melanoma is often a new mole or a change in the appearance of an existing mole.
Normal moles are generally round or oval, with a smooth edge, and usually no bigger than 6mm in diameter.
But size is not a sure sign of melanoma. A healthy mole can be larger than 6mm in diameter, and a cancerous mole can be smaller than this.
See a GP as soon as possible if you notice changes in a mole, freckle or patch of skin, particularly if the changes happen over a few weeks or months.
Signs to look out for include a mole that's:
- getting bigger
- changing shape
- changing colour
- bleeding or becoming crusty
- itchy or sore
The ABCDE checklist should help you tell the difference between a normal mole and a melanoma:
- Asymmetrical – melanomas usually have 2 very different halves and are an irregular shape
- Border – melanomas usually have a notched or ragged border
- Colours – melanomas will usually be a mix of 2 or more colours
- Diameter – most melanomas are usually larger than 6mm in diameter
- Enlargement or elevation – a mole that changes size over time is more likely to be a melanoma
Melanoma can appear anywhere on your body, but they most commonly appear on the back in men and on the legs in women.
It can also develop underneath a nail, on the sole of the foot, in the mouth or in the genital area, but these types of melanoma are rare.
In rare cases, melanoma can develop in the eye. It develops from pigment-producing cells called melanocytes.
Eye melanoma usually affects the eyeball. The most common type is uveal or choroidal melanoma, which grows at the back of the eye.
Very rarely, it can grow on the thin layer of tissue that covers the front of the eye (the conjunctiva) or in the coloured part of the eye (the iris).
Noticing a dark spot or changes in vision can be signs of eye melanoma, although it's more likely to be diagnosed during a routine eye examination.
Read more about melanoma of the eye on our page about eye cancers.