Are there foods I should avoid if I have aphthous stomatitis (canker sore)?

With a canker sores, stay away from hot, spicy or acidic foods. These can irritate the sore. 

Canker sores usually heal on their own after a week or two. Over-the-counter topical anesthetics and antimicrobial mouthwashes may provide temporary relief. Antibiotics from your dentist and some oral bandages can reduce secondary infection.

If you've developed a canker sore (aphthous stomatitis), you may find that avoiding certain groups of food can help, including: 

• spicy foods (e.g. chili peppers and hot sauce)
• acidic foods (vinegar, oranges, grapefruit, and even pineapple)
• salty foods  (nuts, popcorn, peanuts, or pretzels)

All of these foods can cause burning, stinging pain when you have a canker sore. Canker sores also may be triggered by allergies to foods like chocolate, coffee, strawberries, or eggs. If you are allergic or sensitive to these foods, avoiding them will help prevent canker sore outbreaks.

Certain foods seem to trigger or aggravate outbreaks of aphthous stomatitis (canker sore) in some people. If you find that you develop ulcers after eating specific foods or your existing ulcers grow more painful, you should avoid the problem foods. Spicy, salty, and acidic foods can be particularly troublesome. They include (but are not limited to) hot peppers, pretzels, potato chips, citrus fruits (oranges, lemons, grapefruit), and fresh pineapple and tomatoes.