Most malignant melanomas start with a change in normal skin. This can look like an abnormal new mole. Less than a third of melanomas develop in existing moles.

It can be difficult to tell the difference between a mole and a melanoma. However, the following checklist can be used to help. It is known as the ABCD list.

• Asymmetry – Ordinary moles are usually symmetrical in shape. Melanomas are likely to be irregular or asymmetrical.
• Border – Moles usually have a well-defined regular border. Melanomas are more likely to have an irregular border with jagged edges.
• Colour – Moles are usually a uniform brown. Melanomas tend to have more than one colour. They may be varying shades of brown mixed with black, red, pink, white or a bluish tint.
• Diameter – Moles are normally no bigger than the blunt end of a pencil (about 6mm across). Melanomas are usually more than 7mm in diameter.
• Itching, crusting or bleeding may also occur in melanomas – these are less common signs but should not be ignored.
• Normal moles can be raised up from the skin and/or may be hairy.

Very few ordinary moles become melanomas but it is best to discuss any changes in a mole with your doctor, as melanoma can usually be cured if it is found at an early stage.

It is important to see your doctor if you have any unusual marks on the skin that last more than a few weeks, or if you have an existing mole which shows any of the above signs.