The cells that make pigment in the skin are called melanocytes. Usually they are spread out across the skin, with large gaps between them. A mole consists of lots of those cells in one place, without gaps. They commonly appear before the age of 20, but can appear later. The average number of moles on a white-skinned adult’s body is about 30. Factors that determine the number of moles a person has are genetics (whether a person’s parents have lots of moles) and sun exposure in childhood. People who have very many moles, for example over 100, are at an increased risk of melanoma.
The appearance of moles varies greatly. They can be light coloured (especially in fair-skinned people) or dark brown or black (especially in dark-skinned people). Common patterns include being all one colour, or being darker in the centre than at the periphery, or being lighter in the centre than at the periphery.
Approximately half of melanomas develop from pre-existing moles (the other half develop from normal-looking skin). Therefore, if a mole changes in its appearance, it is important to consider whether it could be a melanoma. Abnormalities that should arouse some concern can be summarised as ‘ABCDE’. A stands for asymmetry. B stands for border; an irregular or jagged border can be a sign of melanoma. C stands for colour; a mole that consists of multiple colours. D is for diameter; most melanomas are greater than 6 mm in diameter. E is for evolution; a changing mole. However, many changes in moles are completely harmless. Indeed it is very common for moles to become more raised over time. Bleeding and itching in a pigmented lesion can also be a sign of melanoma.
It is unusual for a new mole to develop after the age of 40; many new lesions after that age are not moles at all, and are instead ‘seborrhoeic warts’ (which are completely harmless), but consideration should be given to the possibility that a new lesion is a melanoma.
The technical term for a mole is ‘melanocytic naevus’. There is a tendency for a person’s moles to look similar to each other, and the term ‘signature naevus’ describes this phenomenon. If a mole stands out as being different from the person’s other moles (an ‘ugly duckling’) it is worthy of closer attention.
Sometimes moles have an appearance that is abnormal, but not abnormal enough to generally indicate melanoma. These moles are referred to as being atypical, and they often have abnormal cells in them; under the microscope they are called ‘dysplastic’. If they are very dysplastic their chance of developing into melanoma is higher than in a normal mole. People who have many moles like this are at a slightly higher risk of developing melanoma.
If you have concerns about a mole then you should immediately see your GP (or a dermatologist). Like most dermatologists, and some GPs, I use a dermatoscope as part of the evaluation of moles (and other lesions). This instrument gives a magnified and deeper view of the lesion.
Harmless moles that are causing a nuisance (for example by catching on clothing), or whose appearance is disliked, can be easily removed by simple surgery. This is done under local anaesthetic (an injection into the base of the mole; you are awake during the procedure). However, the surgery does leave a scar. As a general rule, moles should not be treated by laser therapy.
- 1Spot with hair growth
- 2Round or oval shaped spot
- 3A spot smaller than 1/4 of an inch
Dr Roy Palmer, MBBS, MA, MRCP, PhD
Dr Roy Palmer studied pre-clinical medicine at the Oxford University and qualified as a consultant dermatologist in 2002.