Swollen gums are not a diagnosis by themselves. They are a sign that something underneath needs attention. In many cases, immediate dental treatment matters not because the swelling looks severe, but because the cause may be infection, trapped plaque or progressing gum disease. The National Institute of Dental & Craniofacial Research says gingivitis can make gums red, swollen & easy to bleed & if it is left untreated, periodontal disease can spread deeper as well as affect the bone that supports the teeth.