Bleeding is the first sign of gum disease. When the plaque and calculus (that has bacteria in it) stay attached to the teeth for long time, it irritates and damages the gums and causes gum inflammation. When the gums inflame they bleed! So basically bleeding is the first indication that something wrong is with gums and patient needs to see a dentist. Most of the times, this problem can be treated by professional cleaning and good oral home care by brushing and flossing regularly.