What does this mean?
A mouth ulcer forms when the surface layer of the lining of your mouth is lost over a small, defined area. Its centre is a yellowish grey, ringed by a distinct band of red, and it hurts far more than its size would suggest. Where it settles is fairly predictable: the inside of the lip, the inside of the cheek, under the tongue, the floor of the mouth and the soft palate, in other words the lining that moves and is not bound down to bone. Most ulcers close over within seven to fourteen days without leaving a mark.
What separates this from the problems it resembles is not one sore but the cycle itself. A new one appearing elsewhere before the old one has healed, or another arriving in the same week every month, tells you that what needs looking for lies underneath rather than on the surface of the sore. A sore that stays in exactly the same spot and does not shrink after more than two weeks is a different question; that one no longer belongs here but under the heading of a sore that will not heal. The line between an ulcer and a cold sore is clear too: an ulcer has no blister stage, it does not crust over, and it does not sit on the outer edge of the lip.
More than one factor may be at work behind the recurrence. Low iron, vitamin B12 and folate levels, certain conditions affecting the digestive system, the hormonal cycle, in some people the foaming agents in toothpaste, and stressful periods can all play a part. If they keep coming back in the same place, a sharp edge on a tooth, an overhanging filling or the edge of a denture grazing that spot over and over is also considered. If sores in the mouth come together with sores in the genital area, red eyes or joint symptoms, the picture is not assessed as a condition of the mouth alone.
There is no single cause of mouth ulcers; with recurring ones, what is really being looked for is the background that keeps the cycle going. The headings below bring together the causes most often found in people who get ulcers frequently, along with the conditions that can be mistaken for them.
Likely causes
What helps at home?
- Note where the ulcer appears and the date. If it keeps returning to the same spot, a sharp edge on a tooth, an overhanging filling or a denture edge may be rubbing there, and that is easy to see at an examination.
- While the sore is open, cut down on acidic, salty, hard-crusted and heavily spiced foods; they will not speed up healing, but they do make the pain noticeably worse.
- Do not put aspirin, lemon, bicarbonate of soda or burning home remedies on an ulcer; these can burn the lining, make the sore bigger and delay healing.
- Do not use leftover antibiotics on a mouth ulcer; an ulcer is not a bacterial infection, and medication started without professional advice can upset the natural balance of bacteria in your mouth.
- A sore has passed two weeks without shrinking, or its edges are hardening or becoming raised.
- The ulcers cover much of your mouth and hurt too much for you to take fluids.
- Sores in your mouth come with sores in the genital area, red eyes or joint pain.
- Fever, marked fatigue or unintended weight loss has started at the same time.
- The ulcers have become visibly more frequent in recent months and take longer to heal.
Frequently asked questions
- Are a mouth ulcer and a cold sore the same thing?
- No, they are two different processes. A cold sore begins with small blisters, crusts over and usually sits on the outer edge of the lip. A mouth ulcer has no blister stage, does not crust over, and appears on the moving lining inside the mouth. That is why the two are approached differently.
- Are mouth ulcers contagious?
- Mouth ulcers are not considered contagious; there is no expectation of them passing on through kissing, drinking from the same glass or sharing a fork. Several people in one family getting frequent ulcers is explained less by transmission than by shared eating habits and a family tendency.
- Can a vitamin deficiency really cause mouth ulcers?
- Low iron, B12 and folate are among the things looked into in people who get ulcers often, and a deficiency is found in some of them. Which tests to request, and how any deficiency should be corrected, is a decision for your dentist or doctor. Starting supplements on your own can both mask the real cause and turn out to be unnecessary.
This content is for general information and does not replace an in-person examination. Symptoms overlap between conditions, and a diagnosis can only be made clinically.