 [ Symptoms ] what is vegetable cellulose capsule [ Disease ] canker sores aphthous ulcers are quite common and do tend to be on the inside or mucous membrane of the mouth gums or tongue they tend to be more or less isolated herpes simplex cold sores inside the mouth tends to be multiple cluster like lesions herpetic lesions can also be on the outside of the lips canker sores do not happen on the outside of the lips