When a mouth ulcer does not heal: when to get tested and what is checked

Most mouth ulcers heal within 1 to 2 weeks, but an ulcer that stays longer may not be a simple mouth sore. In Korea, the National Health Information Portal advises that an ulcer that does not respond to 2 to 3 weeks of treatment needs a biopsy to rule out a malignant tumor, and the National Cancer Information Center recommends a biopsy for an ulcer that does not go away after about 3 weeks. A long-lasting ulcer can also have other causes such as a large aphthous ulcer or a repeated injury, so once this criterion is passed, it is safer to sort out the cause by testing.

Published 2026-11-08 · Updated 2026-11-08 · DentalStatics editorial team

Key facts

Ulcer needing a biopsy	An ulcer unresponsive to 2 to 3 weeks of treatment, to rule out a malignant tumor (source: KDCA National Health Information Portal)
National Cancer Information Center criterion	A biopsy is recommended for an ulcer that does not go away after about 3 weeks (source: National Cancer Information Center, National Cancer Center)
Recovery from common ulcers	Pain and ulcers like stomatitis usually disappear in 1 to 2 weeks (source: National Cancer Information Center, National Cancer Center)
Wound after tooth extraction	Mostly heals in 2 weeks; if it hurts for over a month and does not heal, it needs checking (source: National Cancer Information Center, National Cancer Center)
Conditions told apart by blood tests	Systemic diseases such as anemia, leukemia, hemophilia and acquired immunodeficiency syndrome (AIDS) (source: KDCA National Health Information Portal)
Precancerous lesion signals	A white lesion that cannot be wiped off (leukoplakia), a red patch that persists (source: National Cancer Information Center, National Cancer Center)

How long does a mouth ulcer usually take to heal?

Common mouth ulcers heal faster than you might think. The National Health Information Portal explains that aphthous stomatitis heals within 10 to 14 days and herpetic stomatitis usually within 2 weeks without scarring. The National Cancer Information Center also advises that for ulcers like stomatitis, severe pain goes away and the ulcer disappears in about 1 to 2 weeks.

So if an ulcer in the same spot remains beyond 2 weeks, treat it as a course different from usual and watch carefully. If the size is not shrinking or is even growing, get an exam rather than waiting to fill out the full criterion period.

If you cannot remember the date the ulcer began, it is hard to judge against the criterion period. When a wound or ulcer forms in the mouth, a habit of writing the date in a phone note or on a calendar helps.

When should a long-lasting ulcer have a biopsy?

The National Health Information Portal advises that caution is needed when an ulcer does not respond to 2 to 3 weeks of treatment, and that a biopsy should be done to rule out a malignant tumor. This criterion applies to an ulcer that has not improved even though treatment such as ointment or mouthwash has been tried.

The explanation of the National Cancer Information Center points the same way. Simple inflammation heals in 2 to 3 weeks, so if inflammation remains after this time you must get an exam by a specialist at a hospital, and an ulcer that has not gone away after 3 weeks is hard to regard as simple inflammation and becomes a subject for biopsy.

A biopsy is a test in which a part of the ulcer is removed and examined under a microscope. Depending on the result, it distinguishes inflammatory disease, lining disease such as lichen planus and, rarely, precancerous lesions or cancer, and the matching treatment is decided.

What causes a long-lasting mouth ulcer?

There are various reasons an ulcer lasts long. The causes and differential diagnoses confirmed in official sources are below, and because treatment differs entirely by cause, they are told apart by exam and tests.

If the ulcer stays as it is even after fixing the sharp tooth or denture you thought was the cause, it is hard to explain by injury alone. In such cases, a biopsy checks that there is no other cause.

A large aphthous ulcer over 1 cm: lasts from a few weeks to several months by Seoul National University Hospital's medical information
A traumatic ulcer from continual rubbing against a sharp tooth, prosthesis or denture
Chronic lining diseases such as oral lichen planus
Blood diseases such as anemia and leukemia, and weakened immunity
Systemic diseases that repeatedly cause large ulcers, like Behcet's disease
Oral cancer and precancerous lesions

Which signs along with an ulcer call for more urgency?

The National Cancer Information Center explains that unlike cancers in other places, most oral cancer can be recognized by eye, so early diagnosis is relatively easy with regular visits. However, it stresses that early on it can look like a benign tumor, so specialist examination and accurate testing are important. The same material also advises that an oral cancer exam is needed when a lump in the neck under the jaw does not shrink. If the signs below are present with an ulcer, hurry to get care.

A white patch that does not go away when rubbed, or a red patch that stays a long time
A firm feeling around or beneath the ulcer
It bleeds easily or keeps getting bigger
A lump under the jaw or in the neck that does not shrink
The denture suddenly stops fitting
The spot where a tooth was pulled hurts for over a month and does not heal

What do I do while waiting for tests and after them?

Before the exam, put in order the date the ulcer first appeared, changes in size, the medicines used, and whether you smoke and drink. Taking photos of the ulcer by date makes it easier to describe changes in size. If there is a sharp tooth or an ill-fitting denture suspected as the cause, it is sometimes adjusted first and the course watched for a short time.

The National Health Information Portal recommends quitting smoking and drinking and avoiding irritating foods as stomatitis care. When the test results come, treatment matched to the cause begins, and even if it is confirmed to be simple inflammation, return for another visit if an ulcer forms again in the same place.

Common myths and facts

Myth: An ulcer or patch that does not hurt is nothing to worry about.

The National Cancer Information Center explains that precancerous lesions such as leukoplakia often have no symptoms and so are easily not thought of as cancer. If it stays a long time even without pain, it needs checking.

Myth: If you keep applying ointment and wait, it will heal eventually.

The National Health Information Portal advises a biopsy for an ulcer that does not respond to 2 to 3 weeks of treatment. Past this period, confirming the cause comes before continuing treatment.

Myth: If a biopsy is recommended, it means cancer.

The purpose of the biopsy explained by the National Health Information Portal is to rule out a malignant tumor. The test sometimes confirms inflammatory disease or another lining disease.

Frequently asked questions

My mouth ulcer is in its second week. Should I go to the hospital now?

If pain and size are decreasing, you can watch a few more days, but if the size is unchanged or growing, it is better to get examined now. Getting examined in advance lets you move straight to the next step, such as a biopsy, when the 2 to 3 week criterion is passed.

Which department does a biopsy of a mouth ulcer?

A biopsy of a mouth ulcer can be done in oral and maxillofacial surgery or oral medicine at the dentist, or at an ENT clinic. One option is to get examined first at a nearby dental clinic or clinic and, if needed, be referred to a hospital that can do a biopsy. When referred, bring the photos of the ulcer taken so far and a list of the medicines used.

Are smoking and drinking also related to a long-lasting ulcer?

The National Health Information Portal recommends quitting smoking and drinking as stomatitis care, and Seoul National University Hospital's medical information names smoking as one of the local causes of aphthous stomatitis. If you smoke or drink often, tell the clinician at the visit so it can be used as a reference for judging the cause.

Are blood tests also done for a long-lasting mouth ulcer?

When an ulcer lasts long or is frequent, blood tests are sometimes done together. The conditions the National Health Information Portal names to rule out are anemia, leukemia, hemophilia and acquired immunodeficiency syndrome (AIDS), and Seoul National University Hospital's medical information explains that iron, folate and vitamin B12 levels are also checked.

Do I still need regular checkups after the ulcer heals?

The National Cancer Information Center explains that early diagnosis of oral cancer is relatively easy with regular visits. Even after the ulcer heals, ask to have the oral lining looked at too during regular dental checkups, and if it forms again in the same place, compare with earlier records. It is good to keep the biopsy result sheet rather than throwing it away.

References

Korean version →