Alum (aluminum sulfate) is a white, odorless powder commonly found in the spice aisle used for pickling. It is useful for canker sores by causing contraction of tissues to reduce inflammation, and chemically cauterizes the nerves to promote healing and reduce pain.

Alum in a bio-adhesive patch was found in a clinical study to be superior in reducing the size of the ulcer and severity of pain compared to the control group. You can use alum to heal your canker sore with either making a paste or a mouthwash. 

Alum Paste

Use a pinch of alum to mix with a few drops of water to form a paste

• Dab the paste directly on the canker sore for 1 min
• Rinse thoroughly
• You may repeat 3-4 times daily

Because it can hurt significantly when applied directly to the ulcer as a paste, I recommend making a mouthwash if the pain is unbearable, especially for younger children. 

There are some calming teas with healing properties such as chamomile tea that have healing properties, which you can try after you have treated the canker sore with alum.

 Alum Mouthwash

• Boil 2.5 cups of water
• 1 tsp of salt
• ½ tsp of alum
• Rinse and spit, do not swallow

Final Thoughts

Alum is popular as a canker sore treatment because it is readily available, and for some people, works very well to heal the ulcer. Be mindful that because canker sore treatments respond very differently to various people, don't be discouraged if it doesn't work for you. There are many things you can do to help heal your canker sore, including keeping your mouth pH-balanced, maintaining good oral hygiene, and using an alcohol-free mouthwash.