Canker Sore or Cold Sore? How to Tell and When to Worry

Location does most of the sorting. A single crater on the inside of your lip or cheek is almost certainly a canker sore. A cluster of small blisters on the outer edge of your lip is almost certainly a cold sore. One spreads to other people and one does not, and the things that help each are different, so the label matters.

There is a third kind of sore that matters more than either: the one that barely hurts and never leaves. It is uncommon, and it is the reason dentists run an oral cancer screening during checkups.

What is the difference between a canker sore and a cold sore?

The exception to the "inside versus outside" rule

The cold sore virus can occasionally flare inside the mouth. When it does, it appears as a tight cluster of pinpoint blisters or tiny ulcers on the hard palate or the gums, the firm tissue that is bound down to bone. Canker sores almost never form there; they prefer the loose, movable lining. So a patch of small sores on the roof of your mouth a few days after a bad cold is more likely viral than a canker sore.

What triggers a canker sore?

Nobody has pinned down a single cause. What is clear is that canker sores are not something you catch from another person, and that certain things reliably set them off in people who are prone to them:

• Minor injury. A bitten cheek, a toothbrush slip, a sharp tortilla chip, the edge of a bracket or aligner.
• Stress and short sleep. Stress reaches the mouth in other ways too, covered in how stress affects your teeth.
• Acidic or abrasive food. Citrus, pineapple, tomato sauce, sour candy.
• Toothpaste containing sodium lauryl sulfate. The research is mixed, but some frequent sufferers get fewer sores after switching to an SLS-free paste. It is a cheap experiment.
• Hormonal shifts, which is why some women notice a monthly pattern.
• Low iron, vitamin B12 or folate, along with conditions such as celiac disease or inflammatory bowel disease.

Two patterns deserve attention. If a sore keeps returning in the exact same spot beside a chipped tooth, a broken filling or a rough edge, that is a mechanical problem, and smoothing or repairing the edge at a general dentistry visit usually ends it. And if you get sores back to back, several at a time, or unusually large ones, tell your physician. A simple blood test can check for the deficiencies above.

What triggers a cold sore outbreak?

The virus is already there. Herpes simplex type 1 is extremely common: CDC survey data puts it at roughly half of Americans aged 14 to 49, most of whom picked it up in childhood from something as ordinary as a kiss from a relative. Many carriers never get a visible sore. After the first infection the virus sits dormant in a facial nerve and wakes up when something lowers the local defences:

• Strong sun on the lips
• A cold, flu or fever, hence the nickname "fever blister" and the uptick every cold-and-flu season
• Stress and exhaustion
• Chapped or cracked lips
• Hormonal changes
• Trauma to the lip, including having your lips held stretched through a long dental appointment

Most people who get cold sores recognise their own trigger after a few rounds. That is useful, because treatment is all about timing.

What helps a canker sore heal, and what does not

Bluntly: nothing you can buy makes an ordinary canker sore vanish overnight. A small one heals in one to two weeks on its own schedule. What you control is how much it hurts and whether you keep re-injuring it.

Worth doing:

• Rinse a few times a day with warm salt water or baking soda, about half a teaspoon in a cup of water.
• Cover it. Over-the-counter oral pastes and dissolving patches form a barrier so food and teeth stop rubbing the ulcer.
• Use a benzocaine numbing gel right before meals if eating is the hard part.
• Eat cool, bland, soft food for a few days. Skip salsa, citrus, chips and very hot coffee.
• Keep brushing, gently, with a soft brush, and choose an alcohol-free rinse.

Skip these:

• Holding an aspirin against the sore. It causes a chemical burn and leaves you with a bigger wound.
• Dabbing on straight salt, alum or undiluted peroxide. It hurts a great deal, damages the surface, and has no good evidence behind it.
• Alcohol-heavy mouthwash, which stings and dries the tissue.
• Cold sore cream or leftover antibiotics. A canker sore is neither viral nor bacterial, so neither one does anything.

For large, frequent or very painful sores, a dentist or physician can prescribe a topical steroid paste or a medicated rinse. These calm the inflammation and often shorten the course. If you are getting sores every month, ask.

One side effect people don't expect: you brush less thoroughly around a painful spot, and your breath suffers for a week. Odour that lingers after the sore is gone has another cause, and our guide to bad breath that won't go away covers the usual suspects.

What helps a cold sore heal faster?

Antiviral medication, started early. The virus does most of its multiplying in the first day or two, often before a blister is even visible, so treatment that begins at the tingle does far more than treatment that begins at the scab.

• Over-the-counter docosanol cream. Applied five times a day from the first tingle, it trims healing time by roughly a day at best. Modest, but real.
• Prescription antiviral tablets such as valacyclovir or acyclovir. These outperform creams for most people, particularly when taken at the first warning sign. If you get several outbreaks a year, ask your physician or dentist about keeping a prescription on hand so the window doesn't close while you wait for an appointment.
• Plain petroleum jelly to keep the scab from cracking and bleeding, plus a cool compress for the soreness.
• Lip balm with SPF 30 or higher, every day, if sun is your trigger. This one is prevention, and it works.

Leave the crust alone. Picking it restarts the clock and can carry the virus to nearby skin.

How long is a cold sore contagious?

From the first tingle until the skin has completely healed, with the weeping-blister stage the most infectious. Until then: no kissing, no oral sex, and no sharing cups, utensils, lip balm, razors or towels. Wash your hands after touching the sore and keep your fingers away from your eyes, because the same virus can infect the eye.

Be strictest around newborns and anyone with a weakened immune system. A cold sore is a nuisance for a healthy adult and can be dangerous for a baby. The virus can occasionally spread with no sore present, but the risk is far higher during an outbreak. The National Institute of Dental and Craniofacial Research has a plain-language overview of both conditions.

Should I reschedule a dental appointment for an active cold sore?

For a routine visit such as a cleaning, a checkup or whitening, yes, in most cases, as long as the sore is still blistered or weeping. Three reasons. It is contagious, and dental work creates spray. Holding your lips stretched for an hour splits the sore open, which hurts and can spread the virus across the lip. And it heals more slowly afterward.

Call the office instead of simply not showing up, and rebook for when the sore has crusted over and healed, typically about ten days out.

The exception is a real problem. Significant tooth pain, facial swelling or a broken tooth should not wait on a cold sore. Phone, explain both issues, and let the dentist decide how to handle it. If you are unsure whether your situation counts, our guide to what is and isn't a dental emergency will help. And if you tend to break out after dental work, say so before your next long appointment; a preventive antiviral can sometimes be prescribed ahead of time.

A canker sore is different. There is no need to reschedule. Point it out at the start so the hygienist can work around it.

When does a mouth sore need to be examined? The two-week rule

Any sore, lump or discoloured patch in your mouth that has not healed within two weeks should be looked at by a dentist or physician. Canker sores and cold sores both finish their course inside that window. Something that has not is behaving differently, and that alone is reason enough to have it checked.

Duration is the main signal. These features add weight to it:

• It doesn't hurt, or hurts far less than it looks like it should. Canker sores are painful out of all proportion to their size. Early oral cancers frequently are not painful at all, which is exactly why they get ignored.
• It feels firm. A hard or thickened area, or a raised, rolled border around an ulcer.
• A red patch, a white patch, or a mix of the two that does not wipe off.
• It sits on the side of the tongue, under the tongue or toward the back of the throat, which are among the sites where oral cancers most often start.
• It bleeds easily when touched or brushed.
• Something else has changed: numbness in the lip or tongue, a lump in the neck, hoarseness or trouble swallowing that persists, a tooth that has loosened for no reason, or a denture that suddenly fits differently.

Tobacco in any form and heavy drinking raise the risk considerably, and HPV is linked to cancers at the back of the throat. People with none of those risk factors still get oral cancer, though, so the two-week rule applies to everyone. NIDCR's oral cancer page lists the same warning signs.

What the exam is like

Quick. The dentist looks at and feels your lips, cheeks, gums and palate, the top, sides and underside of your tongue, the floor of your mouth, and the sides of your neck. It takes a few minutes and involves no needles and no drilling.

Here is the honest part: the large majority of sores that worry people turn out to be harmless. A canker sore taking its time. An ulcer from a sharp tooth. A sore spot under a denture that needs an adjustment or reline. When something is uncertain, the usual next step is to remove any obvious irritant and re-check in a couple of weeks, or to refer you for a biopsy, which is the only way to diagnose a suspicious spot for certain.

The cost of waiting is lopsided. Having a harmless sore examined costs you a short visit. Sitting on the rare serious one for six months can mean far more involved treatment, because oral cancers found early are considerably easier to treat than those found late.

Not sure what you are looking at?

If a sore has passed the two-week mark, or you would simply like someone to look, call Rio Hondo Dental at (562) 928-5559 or request an appointment at our Downey office. The check takes a few minutes, and se habla español.