Here is something that works extremely well for me. I wet a Q-Tip with oil of oregano and apply it to the canker sore. After the initial stinging, the canker sore dries up and the pain abates. I use diluted (Now Brand) oil of oreagano as undiluted oil of oregano is far too strong to use. I reapply the oil if the pain returns. Some people have a sensitivity to oil of oregano, so use caution. Stress and a lack of sleep can repress the immune system and are thought to be a cause of some canker sores.