The simplest way to tell them apart is location and cause. Cold sores are caused by the herpes simplex virus, are contagious, and appear as fluid-filled blisters that crust over — usually on the outside of the lips or around the mouth. Mouth ulcers (canker sores) are not contagious, are not caused by a virus, and appear as shallow, pale sores with a red rim on the soft tissues inside the mouth. Both are common and usually harmless, but they’re treated differently.
Knowing which one you have helps you treat it correctly and avoid passing a cold sore on to others.
Cold sores at a glance
Cold sores start with a tell-tale tingling, itching or burning a day or so before a cluster of small blisters appears, typically on the lip edge (the vermilion border) or surrounding skin. The blisters weep and then crust over, healing within about seven to ten days. They’re caused by the herpes simplex virus, which most people carry, and they recur when reactivated by triggers. Because the virus is contagious — especially when blisters are present — avoid kissing, sharing drinks, cutlery, towels or lip balm, and don’t touch the sore then your eyes.
Mouth ulcers at a glance
Mouth ulcers form inside the mouth — on the inner cheeks and lips, tongue, or floor of the mouth — as round or oval sores with a white, yellow or grey centre and an inflamed red border. They’re sore, particularly with acidic, spicy or crunchy food, but they aren’t contagious and aren’t viral. Most are “aphthous” ulcers with no single cause, and they heal on their own within one to two weeks.
What triggers each
- Cold sore triggers: sun and wind exposure, stress, illness or fever, tiredness and hormonal changes.
- Mouth ulcer triggers: minor trauma (a cheek bite, sharp tooth or hard toothbrush), stress, certain foods, hormonal changes and low iron, folate or B12.
- Both can flare when you’re run down, which is why they’re sometimes confused.
How to treat them
For cold sores, antiviral creams (and, for frequent or severe cases, antiviral tablets from your pharmacist or GP) work best when started at the first tingle. Keep the area clean, don’t pick the scab, and use a lip balm with SPF to prevent sun-triggered recurrences. For mouth ulcers, soothing measures help while they heal: warm salty-water rinses, a protective gel or paste from the pharmacy, and avoiding acidic, spicy or sharp foods. A soft toothbrush reduces further trauma. Neither usually needs antibiotics.
When to get it checked
See us or your GP if a cold sore is unusually large, spreads, won’t heal in two weeks, or recurs very often. For mouth ulcers, the key guideline is the two-week rule: any ulcer that hasn’t healed within two to three weeks, or that is unusually large, hard, or comes with a lump, should be examined. Persistent sores are usually harmless, but having them checked rules out anything more serious and gives peace of mind.
How we can help
If you get recurrent ulcers, we can check for a sharp tooth, rough filling or denture edge that might be the repeat trigger, and look at whether anything else is contributing. If you’re ever unsure which type of sore you have or one isn’t healing, book an assessment. Patients from Winmalee, Springwood and across the Blue Mountains are welcome.
FAQs
Q: How do I tell a cold sore from a mouth ulcer?
A: Cold sores are blisters on the outside of the lips or around the mouth and are contagious; mouth ulcers are shallow pale sores inside the mouth and are not contagious. Location and whether it blisters are the giveaways.
Q: Are cold sores contagious?
A: Yes. Cold sores are caused by the herpes simplex virus and spread through close contact, especially when blisters are present. Avoid kissing and sharing drinks, cutlery, towels or lip balm until it has healed.
Q: Are mouth ulcers contagious?
A: No. Mouth ulcers (canker sores) aren’t caused by a virus and don’t spread from person to person. They’re usually triggered by minor trauma, stress, certain foods, or low iron, folate or B12.
Q: How long do they take to heal?
A: Cold sores usually heal in about seven to ten days; mouth ulcers in one to two weeks. Any sore that hasn’t healed within two to three weeks should be checked.
Q: What’s the best treatment?
A: Cold sores respond to antiviral creams or tablets started at the first tingle. Mouth ulcers are eased with salty-water rinses and protective gels while they heal. Neither usually needs antibiotics.
Q: When should I see a dentist or doctor?
A: Get checked if any sore lasts beyond two to three weeks, is unusually large or hard, comes with a lump, or keeps recurring. It’s usually harmless, but worth ruling out anything serious.
Not sure what’s going on, or a sore that won’t heal? Book an assessment online or call (02) 7228 8171.
