Gum diseases begin when plaque adheres to the junction between the gums and teeth. If the plaque is not removed every day by brushing and flossing, it hardens into tartar, which can lead to bacterial infection.
The onset of this gum disease is called gingivitis. The gums become red, even though you may not feel any pain. Gradually, the inflammation grows and eventually the gums start to swell.
It is often at this stage that gums begin to bleed when you brush your teeth, although it is not yet painful.
Over time, the inflammation destroys the gum tissue and the underlying bone, so you could lose one or more teeth.