Sonicspeed and all,
There are several things that seem to trigger outbreaks of canker sores, some of which have been mentioned here.
One of the biggies is, as LAELLIS says, toothpastes and/or mouthwashes... the ones that contain sodium lauryl sulfate.
There has been research done that shows using products that contain "SLS", which is a foaming agent, can cause an increased recurrence rate of canker sores. This is probably due to a drying effect it has on the protective surface of oral tissues. When this protective layer has been dried out or damaged in any way, the tissue underneath is more vulnerable to irritants ...like acidic foods for instance.
Then of course there's mechanical trauma. Irritation from a jagged tooth or ill-fitting dentures or a self-inflicted bite etc.
Psychological stress is also a big factor, which we all know.
And of course there are nutritional deficiencies.
Particularly a deficiency in Vitamins B1, B2, B6, B12, and C .
Also researchers have found that low levels of zinc, folic acid, iron, selenium, calcium can contribute to chronic mouth ulcers.
Certain allergies or sensitivities to foods and other substances have also been postulated as being a trigger for canker sore breakouts. Sometimes keeping a diary of what you're eating and comparing it to when you have a "break-out" might help you identify a "culprit".
There's been some research that shows the following potential triggers for cankersores:
Cereal grains: buckwheat, wheat, oats, rye, barley, the gluten protein found in grains
Fruits and vegetables: lemons, oranges, pineapples, apples, figs, tomatoes, strawberries
Dairy: milk, cheeses
Other foods: nuts, chocolate, shellfish, soy, vinegar, mustard
Additives: cinnamonaldehyde (a flavoring agent), benzoic acid (a preservative)
Other "things" like mints, gums, dental materials, metals, and very importantly certain medications.
There is also in some folks, a genetic predisposition for canker sores.
So go thank Mom and Dad! There was one study that found that 91%(!!) of identical twins both suffered from canker sores whereas only 57% of fraternal twins did.
And yes, certain bacteria or viruses can contribute to these ulcers.
Hope some of this info helps.
Obviously if the canker sores become really frequent and troublesome, a check-up with your doctor wouldn't be a bad idea, to rule out any underlying more serious systemic problem.
zuzu xxx