What makes moles itch and bleed?

Moles which stick out a bit can rub on clothes and get a bit sore as a result. If there are a lot of moles doing this, it could be that there's an underlying skin condition that's going on at the some time, so it might be worth Dave going back to his doctor to make sure that everything is otherwise all right. He certainly should try not to scratch - but you would have to scratch regularly for a few years to run the risk of increasing the chance of cancerous change. If you have a sore patch of skin, a break or ulcer of skin then eventually after a number of years that area can become cancerous. But the average bit of trouble or itchy skin or moles is not going to tip the balance into cancer.