If you have a sore inside your mouth, it’s most likely a canker sore, not a cold sore. Cold sores are caused by the herpes simplex virus and almost always form outside the mouth, around the border of the lips. Canker sores are painful white or yellow ulcers that form on the inner cheeks, lips, or tongue. The distinction matters because the treatments are completely different. This guide covers both, so you can figure out what you’re dealing with and treat it effectively.
Cold Sores vs. Canker Sores
The easiest way to tell the difference is location. Cold sores (also called fever blisters) are fluid-filled blisters that appear on or around the lips. They’re caused by HSV-1, a virus that stays dormant in your nerve cells and reactivates periodically. Canker sores only appear inside the mouth and are not caused by a virus. They’re not contagious.
Cold sores start as a cluster of small blisters that eventually break open, ooze, and crust over into a scab. Canker sores look like shallow, round ulcers with a white or yellowish center and a red border. If you see a scab forming, it’s a cold sore. If you see a clean, open ulcer on the inside of your cheek or tongue, it’s a canker sore.
In rare cases, herpes can cause sores inside the mouth, particularly on the gums or hard palate. This is more common during a first-ever outbreak. If you have clusters of small blisters inside your mouth along with fever or swollen glands, that points to an oral herpes infection rather than canker sores.
How Cold Sores Heal on Their Own
Cold sores typically clear up within 5 to 15 days without treatment. They progress through a predictable sequence. First comes the prodrome stage: tingling, itching, or burning at the site, usually hours to a day before anything is visible. Then the skin reddens and swells, forming a small raised bump. Fluid-filled blisters appear next, usually clustered on one side of the lips. After about 48 hours, those blisters rupture, ooze, and form a yellowish crust or scab. The scab eventually falls off as the skin heals underneath.
Everything you do to speed up healing works best when started during that first tingling stage, before blisters form. Once a scab has formed, you’re mostly managing comfort while your body finishes the job.
Over-the-Counter Options
Docosanol (sold as Abreva) is the only FDA-approved nonprescription antiviral for cold sores. Applied five times a day at the first sign of tingling, it can shorten healing time by roughly half a day to a full day compared to doing nothing. In clinical trials, the median healing time was about 4 days with docosanol versus 4.7 days with a placebo. That’s a modest improvement, but starting early gives you the best shot at preventing a full blister from forming. In those same trials, more people who used docosanol had their outbreak abort entirely before reaching the blister stage.
For pain, topical numbing gels containing benzocaine or lidocaine can temporarily dull the soreness. These are available over the counter at most pharmacies. Apply them directly to the sore as directed on the label, and avoid overusing them.
Prescription Antivirals
If your cold sores are frequent or severe, prescription antivirals are the most effective treatment available. Valacyclovir can be taken as a short, aggressive course: two doses twelve hours apart, all within a single day. The key is starting at the very first symptom, during the tingling or burning phase. This one-day treatment can significantly reduce the severity and duration of an outbreak, and in some cases prevent visible blisters from forming at all.
For people who get frequent outbreaks (six or more per year), a doctor may prescribe a lower daily dose taken continuously to suppress the virus and reduce how often it reactivates. If you’re getting cold sores every month or two, this is worth discussing with your provider.
Natural Remedies With Actual Evidence
Most natural cold sore remedies have weak or nonexistent evidence behind them. Lysine supplements are widely recommended online, but a systematic review of natural treatments found that lysine is not well supported by clinical data. The same review noted that most popular supplements “cannot be recommended” based on available trials.
Two exceptions stand out. Propolis, a resin-like substance made by bees, has the strongest evidence of any natural treatment. Six clinical trials found it to be an effective alternative to standard antiviral treatment, with four of those trials finding propolis was actually superior. Honey also showed promise across three trials, though the evidence is less robust. Both are applied topically to the sore. Propolis is available as lip balms and ointments at health food stores.
Other natural options with at least some preliminary trial data include lemon balm extract, tea tree oil, topical zinc, and sage-rhubarb cream. None of these have been directly compared to prescription antivirals in large studies, so they’re best thought of as supplemental rather than primary treatment.
Treating Canker Sores
If what you actually have is a canker sore inside your mouth, the approach is different. Most canker sores heal on their own within one to two weeks. To manage pain, rinse with warm salt water several times a day (about half a teaspoon of salt in a cup of warm water). Over-the-counter oral numbing gels with benzocaine can provide temporary relief when applied directly to the sore.
Avoid acidic, spicy, or rough-textured foods that irritate the ulcer. Switching to a soft-bristled toothbrush and using a toothpaste without sodium lauryl sulfate (a foaming agent linked to canker sore recurrence in some people) can also help. If you get canker sores frequently, a doctor can prescribe a corticosteroid mouth rinse to reduce inflammation.
Common Outbreak Triggers
Because HSV-1 lives permanently in your nerve cells, prevention means reducing how often the virus reactivates. The most well-established triggers include ultraviolet light exposure (sunburn on the lips is a classic trigger), physical or emotional stress, illness or fever, and a weakened immune system. Wearing lip balm with SPF and managing stress can meaningfully reduce outbreak frequency.
Diet may play a role, though the evidence is more limited. The amino acid arginine, found in high concentrations in nuts, chocolate, and seeds, appears to support viral replication. Lysine competes with arginine for absorption, which is the theoretical basis for lysine supplementation. While the supplement data is mixed, reducing excess arginine-heavy foods during periods of stress is a reasonable precaution. Chocolate and other sweets have also been anecdotally linked to outbreaks.
Signs That Need Prompt Attention
Most cold sores are a nuisance, not a danger. But if blisters or sores develop near your eyes or on your eyelids, see a doctor or eye specialist as soon as possible. Herpes can infect the eye (ocular herpes), potentially causing iris inflammation, worsening vision, or in severe cases, rapid vision loss. This is especially urgent in children. Cold sores that spread widely across the face, last longer than two weeks, or occur alongside a high fever and difficulty swallowing also warrant medical evaluation.