When people don't practice proper dental hygiene, bacteria in the mouth forms plaque on the teeth. These bacteria may cause your gums to become inflamed, which results in red, swollen, or bleeding gums. For many people with gingivitis, this inflammation is not painful. If you catch gingivitis early, it can be reversed and healed with proper oral hygiene. But left untreated, gingivitis can worsen and ultimately lead to tooth loss.