Moles 

Moles, also known as melanocytic naevi, are small skin lesions that are usually brown. They are a collection of cells called melanocytes, which produce the pigment (colour) in your skin.

Moles are usually a brownish colour, although some may be darker or skin-coloured. They can be flat or raised, smooth or rough and some have hair growing from them. Moles are usually circular or oval with a smooth edge.

Moles can change in number and appearance. Some moles fade away or fall off over time, often without you realising. They also sometimes respond to hormonal changes, for example during:

• pregnancy: when they may get slightly darker
• the teenage years: when they increase in number
• older age: when they may disappear from 40 to 50 years of age onwards

When do moles develop?

Some moles, known as congenital melanocytic naevi, are present at birth. However, most moles develop during the first 30 years of life. These are called acquired melanocytic naevi. People with fair skin often have more moles than people with darker skin.

Most moles have a genetic cause and are inherited. This is often the case with people who have a lot of moles. Where you were brought up may also make a difference,. For example, if you have been in the sun a lot for many years you may have an increased number of small moles.

People who spend a considerable amount of time in the sun often develop brown marks on their skin, especially the face and arms. These tend to be sun spots or solar lentigines and appear later on in life. Severe sunburns on the shoulders, for example, may also cause some sun spots which are not moles.

See the Health A-Z topic about Sunburn for more information.

Malignant melanoma

Most moles are harmless, but in a few rare cases they can develop into malignant melanoma, which is an aggressive form of skin cancer.

Malignant melanoma is the most serious type of skin cancer. The cause of melanoma is complex and is usually explained by a mix of genetic factors and the environment, mainly exposure to the sun. However, many melanomas are not caused by excessive sunbathing and may occur on parts of the body that have not been exposed to much sun. 

Malignant melanoma can appear anywhere on the body. It may be a dark, fast-growing spot where there was not one before, or a pre-existing mole that changes size, shape or colour and bleeds, itches or reddens. However, the bleeding, crusting and itching are late signs and ideally melanoma should be diagnosed earlier. Itching is also not a very specific sign, as benign (non-cancerous) moles may itch occasionally.

See the Health A-Z topic about Malignant melanoma for more information.

Harmless moles

You should check all your moles every few months for any changes. A change in a mole may occur in weeks but in some moles it may occur in months. See Moles - prevention for information and advice about checking your moles and the changes to look out for. If there are no changes it is not a melanoma, as a melanoma will change with time.