Bleeding gums is the first sign of gum infection-gingivitis. Plaque is a biofilm that forms on the tooth surfaces and on prosthesis. When this plaque is not removed by proper brushing and flossing, it gets hardened by the calcium in the saliva. This tartar harbours many bad bacteria that damage the gums. This causes inflammation or redness and bleeding from the gums. Brushing, biting on hard food, applying pressure on the gums and sometimes flossing can cause the gums to bleed.