How can one break the habit of biting themselves?

Breaking habits: To make or break any habits, medically speaking we need three weeks (21 days). Theoretically speaking, it takes 21 days to make a new neural pathway! any new habit to form or break, it has to be engraved into our body system as a neural pathway. Once it is engraved ( 21 days); then we don't need extra efforts to work on it. This means only three weeks of effort--- keep checking on yourself!