Updated in September of 2026
A mouth ulcer is a small, painful sore that forms inside your mouth, on your cheeks, lips, tongue, or gums. Most people call the common type a canker sore, and while they are usually harmless, they can make eating and talking uncomfortable until they heal.
What Causes a Mouth Ulcer?
Doctors do not know the exact cause of most mouth ulcers, but a few things tend to trigger them. Common triggers include minor injury from biting your cheek or brushing too hard, acidic or spicy foods, emotional stress, and a diet low in vitamin B12, zinc, folate, or iron, according to Mayo Clinic. If you get mouth ulcers often, it is worth mentioning to your dentist, since recurring sores sometimes run in families.
How Long Does a Mouth Ulcer Last?
Most mouth ulcers heal on their own within one to two weeks. Larger or deeper ulcers can take up to six weeks to fully heal and may leave a small scar. If your ulcer lasts longer than two weeks without improving, it is a good idea to have it checked.
How Do You Treat a Mouth Ulcer at Home?
You can ease the pain of a mouth ulcer while it heals with a few simple steps. Rinse your mouth with warm salt water a few times a day, avoid acidic, spicy, or crunchy foods that irritate the sore, and try an over-the-counter numbing gel if you need extra relief. Applying a cold, wet tea bag directly to the ulcer can also help calm the pain.
Canker Sore or Cold Sore: What Is the Difference?
Not all mouth ulcers are the same. Canker sores form inside the mouth, are not contagious, and are not caused by a virus. Cold sores, on the other hand, form on or around the outside of the lips, are highly contagious, and are caused by the herpes simplex virus. Cold sores usually need an antiviral medication to treat them, so it helps to know which type you are dealing with before you try to treat it at home.
When Should You See a Dentist About a Mouth Ulcer?
You should call your dentist if a mouth ulcer lasts more than two weeks, keeps coming back, or is unusually large or painful. You should also reach out if the pain is not controlled by home care, if you have a hard time eating or drinking, or if you develop a fever along with the sore. A sharp tooth or dental appliance rubbing against the same spot repeatedly can also cause ulcers, and your dentist can help fix that underlying cause.
Call Harlow Dental With Any Concerns
If a mouth ulcer is not improving, keeps coming back, or is causing you significant pain, give your Charlotte, NC dentist a call. Dr. Justin Harlow and our team at Steele Creek, 7th Street, or Eastway are happy to take a look and help you find relief.