I have had loads of brown moles since I was a child, and they don't seem to have changed much. However, friends say they should be checked for cancerous changes. What are the signs that should send me to the doctor?
First, the vast majority of moles remain benign, so don't be anxious. But you do need to recognise when one is starting to go wrong. Look for changes in size, shape and colour: we see them as the major signs. Minor signs are reddening and swelling, crusting and bleeding; a "different" feel to it, including pain or itch; and a diameter of 7mm or more. They can all start in a flat or lumpy "mole" (the correct name is naevus). If you have one or more of the majors, along with one or more of the minors, please go to see your doctor. Usually a malignant melanoma has an irregular edge (sometimes with "satellite spots" around it), and the depth of the surface colour varies. Get to know your moles so that you will notice changes if they occur. It is easier than you think.

• Do you have a question for Dr Smith? Email doctordoctor@guardian.co.uk