Gingivitis is a response by the gum tissue caused by plaque building up around the gum line surrounding your teeth. If your brushing and flossing technique is not satisfactory, plaque will build-up at the junction where the teeth come through the gums. This will aggravate the gums causing them to become inflamed, red and swollen, you may also notice they bleed when you brush your teeth.
Gingivitis is a reversible condition and effective cleaning will lead to healthy gums in a couple of weeks. If you have gingivitis and you do not address the issue, it may develop into periodontitis, otherwise known as gum disease and is associated with irreversible loss of teeth and underlying bone.