Finding a sore in your mouth can be unsettling. Many mouth sores are caused by irritation or common conditions and improve on their own. The important question is whether the area is healing as expected or needs an examination.
How long is too long?
Common canker sores and cold sores often heal within one to two weeks. The National Institute of Dental and Craniofacial Research advises seeing a dentist or physician if a sore, lump or unusual patch lasts more than two weeks. You do not need to wait that long if a change is worsening or concerning.
The American Dental Association's updated 2026 guideline also emphasizes follow-up: if a lesion has not resolved 10 to 14 days after an initial clinical evaluation and there is no definitive diagnosis or treatment plan, prompt biopsy or referral is recommended. That is a follow-up standard, not a reason to delay the first appointment.
What can cause mouth sores?
Possible causes include a cheek bite, a sharp tooth or filling, a poorly fitting dental appliance, canker sores, cold sores, infections and inflammatory conditions. Canker sores are usually painful ulcers inside the mouth and are not contagious. Cold sores generally occur around the outside of the lips and are contagious.
Appearance alone may not establish the cause. A painless area is not automatically harmless and a painful area is not automatically serious. Persistence, progression and examination findings matter.
Which changes should be examined?
Tell your dentist about a sore that does not heal, a persistent red or white patch, a lump or thickened area, unexplained bleeding or numbness, or changes in chewing and swallowing. Many such symptoms have noncancerous explanations, but they should not be diagnosed from photographs alone.
What happens at the appointment?
The dentist asks when the change began, whether it is improving, and whether there has been trauma, a new oral-care product or another relevant health change. The examination may include looking and gently feeling the mouth, tongue, lips and neck. Depending on the findings, the dentist may address an obvious source of irritation and schedule a recheck or recommend prompt specialist evaluation or biopsy.
Learn more about our oral cancer screening examination.
Can a special light or saliva test rule out a serious problem?
No. The ADA's 2026 living guideline advises that adjunctive tests should not replace clinical judgment or an indicated biopsy or referral. A biopsy with laboratory examination is the diagnostic standard when a suspicious lesion requires it.
Before your visit
Note when you first noticed the area and whether it has changed. A dated photograph may help describe its course. Mention sharp teeth, appliances, recent dental work, medications and new products. Avoid repeatedly picking at the sore. If you have a persistent or changing area, request an appointment for evaluation.
Sources
ADA: Oral Cancer Guideline (2026 Update)
NIDCR: Fever Blisters and Canker Sores
This article provides general education and does not replace an individual examination or diagnosis.
