There are many reasons for the lumps on the inner wall of the mouth with pain and odor, such as periodontal abscess, mucous cyst, parotid cyst and so on. 1. Periodontal abscess: periodontitis can induce periodontal abscess, resulting in the phenomenon of lumps on the inner wall of the mouth, accompanied by pain and odor. 2. Mucous cysts: Mucous cysts are salivary adenomatous lesions, which also cause bumps on the inner wall of the mouth with pain and odor. 3. Parotid cysts: parotid cysts belong to benign tumors in the oral cavity, due to the blockage of parotid ducts, resulting in the retention of secretions, so that the gradual expansion of the formation of cysts, so there will be a lump on the inner wall of the mouth with pain and a little bit of odor. There are many other reasons why the wall of the mouth lumps with pain and a little bit of odor, after the appearance of symptoms, it is recommended to go to the hospital in a timely manner to improve the examination, under the guidance of the doctor to take standardized treatment, do not ignore the symptoms, to take it lightly.