Bleeding gums are a sign of gum disease. It is not normal for your gums to bleed. Please read our page on gum disease to understand more about this problem. What happens is that you have plaque on your teeth near the gums and under them, which irritates the gums and makes them prone to bleeding.
Often, the tendency is to avoid brushing or flossing areas that bleed because that is what tends to make them bleed. This, however, will only aggravate the problem. Keeping the teeth clean keeps the irritants away and will help the gums next to the teeth heal. Letting plaque and other irritants accumulate makes it impossible for the gums to heal.
If your gums bleed, it usually takes about two weeks of faithful brushing and flossing for them to heal and quit bleeding. Conditions of elevated hormone levels, such as pregnancy, will make the gums be more sensitive to irritants and more prone to bleeding. The best response to these situations is to be extra diligent in keeping your teeth clean.
—Dr. David Hall.
Other information about tooth sensitivities and related subjects: