Cold sores are symptoms of a virus and can be awfully painful. As with any virus, these sores run their course in about 7 to 10 days. If these sores appear on or about your lips, keep them moist with some petroleum jelly. Your dentist will be able to help with a new prescription drug especially for these sores. If the sores aren't gone within 7 to 10 days, or worsen, call your dentist!