Gum swelling and pus may be severe periodontitis, chronic periapical periodontitis, pericoronitis, etc. 1. Severe periodontitis: when periodontitis is severe, periodontal abscess may appear, excessive inflammation, leukocyte accumulation and necrosis may cause swollen and pus-filled gums. 2. Chronic apical periodontitis: As the tissues around the root apex show an inflammatory reaction, the white blood cells coalesce and become pus-filled, and then drain out from the surrounding gums, which may result in swollen, painful and pus-filled gums. 3. Pericoronitis: often occurs in the gums around the blocked wisdom teeth, inflammation will cause swelling and pus in the gums. Gum swelling and pus may also have other reasons, it is recommended to go to the hospital in a timely manner, improve the examination to clarify the cause of the disease, under the guidance of the doctor to give targeted treatment or treatment.