The short answer
Most mouth ulcers are harmless canker sores or from a bite or irritation, and they heal within about two weeks. A mouth sore, ulcer, or red or white patch that does not heal within three weeks can occasionally be a sign of mouth cancer and is worth checking.
Most mouth ulcers are harmless and heal within two weeks.
A sore or patch that does not heal within three weeks is worth checking.
Red or white patches or a lump in the mouth are more worth checking.
Risk is higher for people who smoke, chew tobacco, or drink heavily.
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The full explanation.
The simple version
Mouth ulcers are very common and almost always harmless — canker sores, a cheek bite, braces rubbing, or a viral infection. They usually heal on their own within a week or two. A sore that does not heal, though, is the pattern worth checking.
What usually causes mouth ulcers
Common causes include canker sores (aphthous ulcers), accidental bites, sharp teeth or dentures rubbing, viral infections, stress, and some deficiencies. These typically heal within two weeks once the irritation settles.
When a mouth sore is more worth checking
A mouth problem is more worth a doctor's or dentist's look when a sore or ulcer does not heal within about three weeks, or there is a red or white patch that will not go away, a lump or thickening, ongoing mouth pain, a numb area, or trouble swallowing. Risk is higher for people who smoke, use chewing tobacco, or drink heavily.
When to see a doctor or dentist
See a doctor or dentist about any mouth sore, ulcer, or patch that does not heal within about three weeks, or a persistent lump. Dentists often spot these early during check-ups, so regular visits help.
Words to know
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Common questions
▸Does a mouth ulcer mean mouth cancer?
Almost never. Most mouth ulcers are harmless canker sores or from irritation and heal within two weeks. A sore that does not heal in three weeks is worth checking.
▸When should a mouth sore be checked?
When it does not heal within about three weeks, or there is a red or white patch, a lump, ongoing pain, or numbness.
▸Who is at higher risk of mouth cancer?
People who smoke, use chewing tobacco, or drink heavily are at higher risk and should get non-healing sores checked.
▸Can a dentist help?
Yes. Dentists often spot mouth problems early during check-ups, so regular dental visits are useful.
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