There are many reasons for the swelling of a bag on the upper lining of the mouth, such as traumatic ulcers, oral herpes, hand, foot and mouth disease. 1. Traumatic ulcers: due to mechanical stimulation and other factors can lead to oral mucosal injury, thus appearing in the mouth above the inner wall of the phenomenon of a bag, but also may be accompanied by redness, swelling, ulceration phenomenon. 2. Oral herpes: oral infection with herpes simplex virus can induce the phenomenon of a swollen bag on the upper lining of the mouth, accompanied by pain, herpes rupture can form ulcers. 3. hand, foot and mouth disease: hand, foot and mouth disease is due to enterovirus infection, can lead to the patient’s hands, feet, mouth are skin lesions, accompanied by oral mucosa blisters, so there will be the phenomenon of the upper lining of the mouth swollen a bag. There are many reasons for the swelling of a bag on the upper lining of the mouth, after the appearance of symptoms, it is recommended to go to the hospital in a timely manner to improve the examination, a clear diagnosis under the guidance of the doctor to take standardized treatment, do not take the treatment, so as not to lead to adverse consequences.