Information for Patients: Canker Sores

Canker Sores (Aphthous Ulcers to the dental folk) are the most common mouth ulcers and affect one-fourth of the population world-wide.

What Causes Them?

The cause is not known exactly, but it seems to involve the patient having an excess immune response (similar to an allergy) to certain normal bacteria on the skin in the mouth. Minor injuries in the mouth, emotional stress, food allergies and hypersensitivity or allergy to toothpaste ingredients may play a part, too. Aphthous ulcers can be worse when acid foods like citrus fruits and tomatoes are in season.


Most toothpastes contain the foaming agent sodium lauryl sulphate, or SLS, which has been found to cause irritation in sensitive mouths. Toothpastes containing SLS should be avoided if you have sore mouth (mucositis), oral ulcers or dry mouth. Biotene ‘Dry Mouth Toothpaste’ is SLS free, contains fluoride and important salivary enzymes.  MI paste and Rembrandt ‘Natural’ are also SLS free.

What Should the Patient Do?

The treatment of canker sores is to make the patient comfortable. There isn’t a cure, unfortunately. Oral Rinses such as Benadryl with Kaopectate are good for mild, widespread or inaccessible ulcers. Chlorhexidine-containing rinses (Peridex) can also be helpful, as can Tetracycline solutions.

An ointment such as Zilactin B can help cover the sores and let them heal. Lidex gel .05% (fluocinamide) is another good choice to block the pain if you can reach the spots with a Q-tip. For worse cases, Kenalog in Orabase can be prescribed. The treatment is to apply a thin film to the canker sore after each meal and at bedtime. Use a wet Q-tip. This works very well.

A powerful prescription to prevent flareups in patients who get lots of ulcers is Decadron Elixir 0.5mg/5ml. For this medication, you rinse twice daily with 1-2 tsp. DO NOT SWALLOW!

How can you avoid them?

To reduce aphthous ulcers, avoid spicy foods and acid foods like citrus fruits and raw tomatoes. Also avoid Tartar-control toothpastes. Very sensitive patients may need to avoid sodium lauryl sulfate, a very common toothpaste ingredient. Some special toothpastes (eg. Biotene and MI paste) do not have this ingredient.

For more thorough information, you may visit Dr. Kent Smith’s website.