Hydrogen peroxide Found at your pharmacy, hydrogen peroxide may also be used as an effective mouthwash. Swish a capful around in your mouth twice a day and spit out. Another remedy says to use three parts water to one part hydrogen peroxide. Hydrogen peroxide is very good at killing bacteria, but use it sparingly when needed unless recommended by your dentist. It can kill too many good bacteria and cause other dental problems.
Onion Apply raw onion to the sore.
Papaya Cankers can be cleared up by sucking on or chewing several papaya tablets a couple of times each day. Fresh papaya fruit would be good, too, if you can find it, and, if you live where there are fresh papaya leaves, chew on them. Plum juice Take two tablespoons of fresh plum juice and use it as a mouth rinse for several minutes. For a bad sore soak a cotton ball in plum juice and use it as a compress for a few minutes. At the first sign of a canker sore, gargle with a mixture of 1 teaspoon soda and a pinch of salt in 1 cup of warm water.