A small, round, painful white or yellow ulcer with a red border inside your mouth — on the cheek, tongue, or gum — is a canker sore (aphthous ulcer). Unlike cold sores, they aren't contagious or caused by a virus, and most heal on their own within 1 to 2 weeks. The most useful step is soothing care: avoid acidic and spicy foods and use an over-the-counter numbing gel or rinse. For large or recurrent sores, a clinician can prescribe a stronger topical treatment. A licensed clinician can review your symptoms online and send a prescription to your pharmacy the same day when needed.
Seek emergency care if: a sore is larger than 1 cm, lasts more than 3 weeks, or is painless and persistent — get an in-person exam to rule out oral cancer. Fever with multiple ulcers and a rash also needs evaluation.
See a clinician nowWhat is canker sores?
Canker sores (aphthous ulcers) are small painful round or oval ulcers inside the mouth — on cheeks, gums, tongue, or lip. Affect about 20% of US adults. Not contagious and not related to herpes (cold sores).
Most resolve on their own in 1–2 weeks. Prescription topical treatments help with pain and speed healing. Frequent severe cases may benefit from systemic evaluation.
Do I have canker sores? Common signs
If most of these describe what you're experiencing, telehealth may be a good next step:
What causes it
Unknown but linked to stress, oral trauma (biting cheek, dental work), certain foods (acidic, spicy), vitamin deficiencies (B12, iron, folate), hormonal changes, SLS in toothpaste, gluten sensitivity, some medications. Family history common.
Is it contagious?
No.
If you get more than 3 per year, ask about B12, iron, and folate — deficiency drives many recurrent cases.
Can it be treated online?
Routine canker sores are well-suited to telehealth. Frequent or severe cases benefit from systemic workup (vitamin levels, celiac, IBD). Lesions lasting >3 weeks, very large, or atypical need in-person evaluation to rule out oral cancer.
How canker sores is treated
Topical steroids: triamcinolone in Orabase, fluocinonide gel — applied 3–4x daily speeds healing. OTC options: benzocaine, hydrogen peroxide rinse, sodium bicarbonate rinse. Chlorhexidine rinse for recurrent cases. Treat underlying vitamin deficiencies. Severe recurrent cases may need colchicine or prednisone.
Self-care while you wait
- Avoid acidic, spicy, crunchy foods during flare
- SLS-free toothpaste
- Salt water or baking soda rinses
- Honey topically
- Ice the area for pain
- Use vitamin B12, iron, folate if levels low
- Manage stress
- Avoid mouth trauma
How long does it last?
Individual sores: 7–14 days. Recurrent in many people, often monthly.
Frequently asked questions
Are canker sores the same as cold sores?
No. Canker sores are inside the mouth, not contagious, not herpes. Cold sores are on/near lips, caused by HSV-1.
Why do I keep getting them?
Common triggers: stress, dental work, SLS toothpaste, certain foods, vitamin deficiencies, hormonal cycles.
Is it serious?
Usually no. Persistent or unusual ulcers should be evaluated to rule out oral cancer, immune conditions, or systemic disease.
Will any vitamin help?
B12, iron, folate, zinc deficiencies are linked. Reasonable to check levels if recurrent.
Can I use Listerine?
Alcohol-based rinses can sting and aren't proven to help. Salt water or alcohol-free rinses are better.
