A swollen bag on the right side of the inside of the mouth may be caused by bite wounds, mucous gland cysts, herpetic stomatitis and so on. 1. Bite wounds: when the bite relationship is not good or bad bite, accidentally biting the inner mucosa of the mouth, there can be capillary rupture to form a blood blister, which causes the right inner wall of the mouth inside a swollen bag phenomenon. 2. Mucous gland cysts: a benign tumor commonly found in the oral cavity, manifested as a limited mass, usually accompanied by biting pain. It is mainly caused by mucous gland retention. 3. Herpetic stomatitis: small blisters, oral pain and other symptoms may also appear in other skin-mucous membrane junction. There are other possibilities, such as oral cancer, etc. It is recommended to consult a doctor in time to find out the cause and treat the cause.