There are two main forms of gum disease gingivitis & periodontal disease.
In gingivitis the gums around the teeth become very red, swollen & inflamed. They will frequently bleed when they are brushed during cleaning. The earliest signs of gum disease are usually blood on your toothbrush or in the water when rinsing your mouth after cleaning your teeth. Bleeding from the gums can also occur when eating, although you are unlikely to experience any pain or discomfort. You may also notice an unpleasant taste in your mouth or bad breath as a result of any bleeding. Over time, gingivitis can develop into periodontal disease. When this happens the bone supporting the teeth is destroyed, making the teeth loose. You may also begin to experience abscesses with pus oozing out of pockets around the teeth. Eventually, if the condition is not treated, the teeth will fall out or need to be extracted.
Both types of gum disease are caused by plaque, which is the film of bacteria that builds up on your teeth. In order to prevent and treat gum disease, it is essential that all of this plaque is removed from your teeth at least twice a day. This means you not only need to brush your teeth, but also clean in between them using floss or "interdental brushes".