Canker sores vs cold sores
Canker sores and cold sores look similar but are different. Learn the differences and how to treat them.
Medically reviewed by Dr. Jose — June 8, 2026
Canker sores form inside your mouth and aren’t contagious. Cold sores are on your lips/outside mouth, caused by herpes virus, and are contagious.
Differences
| Canker Sore | Cold Sore |
|---|---|
| Inside mouth | On/around lips |
| Not contagious | Contagious |
| Round, white/yellow center | Fluid-filled blisters, then crust |
| Caused by: mouth injury, acidic foods, stress, canker-prone condition | Caused by: herpes simplex virus (HSV-1) |
| Last 1–2 weeks | Last 7–10 days |
Home treatment
- Salt-water rinses — several times daily
- Topical numbing gel — for pain relief
- Avoid acidic/spicy foods — citrus, tomato, hot peppers irritate
- Don’t pick at it — let it heal
- Cold compress — may soothe pain
When to see a dentist
- Sore larger than 1/2 inch
- Sore lasts beyond 2–3 weeks
- Multiple sores appearing together
- Sore causes extreme pain or difficulty eating
Prevention
- Avoid triggers — if certain foods cause canker sores, skip them
- Use soft toothbrush — avoid injuring mouth tissue
- Manage stress — canker sores are often stress-related
- Antiviral medication — if you get frequent cold sores, ask your doctor about preventive treatment
Frequently asked questions
How long should a mouth sore last?
Most canker sores heal in 1–2 weeks. Cold sores take 7–10 days. If a sore persists beyond 2 weeks, see a dentist.
What's the best treatment?
Topical numbing agents and salt water rinses help. Cold sores can be treated with antivirals (prescription). Most heal on their own.