Cold Sore vs Canker Sore: How to Tell the Difference and Treat Each One
Written by Cherlie Joseph, MSN, FNP-BC · Medically reviewed by Naurah Gaspard, DNP, FNP-C, FNP-BC · Updated November 2026
Location is the quickest clue. Cold sores are clusters of blisters on the outside of the lips or around the mouth, caused by the herpes simplex virus and contagious. Canker sores are single round ulcers with a white or yellow center inside the mouth, on the cheeks, gums or tongue; they are not caused by herpes and are not contagious. Cold sores respond to antivirals, while canker sores usually heal on their own in 1 to 3 weeks.
In this guide
Side-by-side comparison
| Cold sore | Canker sore | |
|---|---|---|
| Where | Outside: lip border, corners of mouth, under the nose | Inside: inner lips and cheeks, tongue, base of gums, soft palate |
| Looks like | Cluster of small fluid-filled blisters that crust over | Round or oval ulcer, usually under 1 cm, white or yellow center, red rim |
| Warning before | Tingling, itching or burning a day before | Sometimes mild burning |
| Cause | Herpes simplex virus (usually HSV-1) | Not fully known; injury, stress, low iron, B12 or folate, hormones, some foods |
| Contagious? | Yes, until fully healed | No |
| Healing time | 7 to 10 days | Pain fades in 7 to 10 days; full healing 1 to 3 weeks |
| Main treatment | Antiviral pills such as valacyclovir, started early | Comfort care, numbing gels, rinses; steroid paste for severe cases |
What causes each
Cold sores come from herpes simplex virus type 1, which the World Health Organization estimates infects about 64% of people under 50 worldwide. The virus stays in nerve cells and reactivates with sun, stress, illness, fever, hormonal changes or dental work.
Canker sores are not an infection. MedlinePlus lists common triggers:
- Mouth injury: biting your cheek, dental work, braces, aggressive brushing
- Stress and hormonal changes, such as around periods
- Low iron, folic acid or vitamin B12
- Food sensitivities
- A family tendency; they are more common in women
Frequent or severe canker sores can be linked to celiac disease, inflammatory bowel disease or other immune conditions, which is why repeat sores are worth a checkup. If low iron is a concern, see our guide to iron deficiency in women.
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- Start a prescription antiviral such as valacyclovir at the first tingle; it works best early.
- Over-the-counter docosanol (Abreva) helps modestly if used from the start.
- Cool compresses, pain relievers as the label directs, and petroleum jelly for cracking.
- Do not pick or pop; avoid kissing and sharing items until healed.
- Use SPF lip balm daily to prevent sun-triggered outbreaks.
More details: cold sore treatment and cold sore stages.
Treating a canker sore
Most canker sores heal on their own. These steps ease pain while they do:
- Rinse with salt water or an alcohol-free mouthwash.
- Use an over-the-counter numbing gel (benzocaine) or a protective paste as the label directs.
- Avoid hot, spicy, salty and acidic foods, and crunchy foods like chips.
- Take acetaminophen or ibuprofen as the label directs.
- Use a soft toothbrush, and consider toothpaste without sodium lauryl sulfate if you get them often.
For large, very painful or frequent sores, a provider may prescribe a steroid paste or rinse, or a chlorhexidine mouthwash, and may check iron, B12 and folate.
Other mouth sores to know about
- First herpes infection (herpetic stomatitis): many painful sores on the gums and inside the mouth, with fever.
- Hand, foot and mouth disease: mouth sores plus spots on the hands and feet; common in kids but adults get it too.
- Oral thrush: white patches that can be wiped off, leaving red skin.
- Angular cheilitis: cracks at the corners of the mouth, often from yeast or saliva buildup.
- A sore that will not heal: any mouth sore lasting more than 2 to 3 weeks needs to be checked, as it can rarely be a sign of oral cancer.
Get in-person care or call 911 if you have:
- A sore near your eye, or eye pain or vision changes
- High fever, severe headache or confusion with mouth sores
- Not being able to drink enough fluids because of mouth pain
- Mouth sores with a rash, blisters or peeling skin elsewhere on your body
- A mouth sore that has not healed in 3 weeks
Frequently asked questions
Can a cold sore be inside your mouth?
Recurring cold sores almost always appear on the outside of the lips. Sores inside the mouth are usually canker sores, except during a first herpes infection, which can cause many sores on the gums and inside the mouth.
Are canker sores contagious?
No. Canker sores are not caused by a virus that spreads to others, so you cannot pass them on by kissing or sharing drinks.
What gets rid of a canker sore fast?
Salt water rinses, numbing gels and avoiding spicy or acidic foods ease pain, but most sores still take 1 to 2 weeks to heal. A provider can prescribe a steroid paste for severe sores.
Sources
- MedlinePlus: Canker sore
- MedlinePlus: Cold Sores
- World Health Organization: Herpes simplex virus fact sheet
Keep reading
- Cold sore treatment: valacyclovir and Abreva
- Cold sore stages
- Sore throat remedies
- Browse all conditions and treatments A to Z
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Cherlie Joseph, MSN, FNP-BC
Board-certified family nurse practitioner licensed in Florida, caring for adults online at OurTopClinic. Meet our providers.
This article is for general education and is not a substitute for medical advice. Treatment, including any prescription, is decided by a licensed provider after reviewing your health history. OurTopClinic is not for emergencies; if you have a medical emergency, call 911. OurTopClinic serves adults located in Florida, New Mexico, Oregon and Washington. Learn more at ourtopclinic.com.
