There are many reasons why a soft bump grows on the gums of a bad tooth, mainly related to periodontal abscess, apical periapical fistula, gum tumors and so on. 1. Periodontal abscess: usually on the side of the affected tooth will form a swollen bump, gums red, edema, shiny surface and accompanied by severe pain. 2. Periapical fistula: usually occurs in chronic periapical inflammation, more buccal side of the gums appear small pus or pus will have small eyes. 3. Gum tumor: some tumors around the gums such as gingival tumor, gingival fibroma, etc., will also form a round or oval lump on the surface of the gums. There may be other reasons for the gums of bad teeth to grow a soft bag, such as gingivopapillitis, gingival hyperplasia, etc. It is recommended to consult a doctor in time, complete the relevant examinations, and carry out targeted treatment and therapy after clarifying the cause of the disease.