Natural remedies aren't just a great way to save money, they are a safe and effective way to treat canker and cold sores. The oldest natural remedy, and yes it. Natural Remedies. Stay Away from Citrus Certain foods can cause and irritate canker sores, so it's best to stay away from these while you're trying to heal. Your sweet baby or toddler dealing with a painful canker sore? Here's what causes them and home remedies to treat these mouth ulcers.