Cold sores typically appear on or around the lips, not inside the mouth. If you have a sore inside your mouth, it’s most likely a canker sore, which is a completely different condition with different treatment. That said, the herpes simplex virus can occasionally cause sores on the gums or hard palate, and standard cold sore treatments still apply in those cases. Knowing which type of sore you’re dealing with is the first step toward treating it effectively.
Cold Sores vs. Canker Sores
These two conditions look different and behave differently. Cold sores are clusters of small, fluid-filled blisters caused by the herpes simplex virus. They almost always show up on the outside of the mouth, along the border of the lips. Canker sores appear inside the mouth and are typically a single round sore that’s white or yellow with a red border. Canker sores are not caused by a virus and are not contagious.
If what you’re seeing inside your mouth is a single round ulcer on the inner cheek, tongue, or soft tissue, that’s almost certainly a canker sore. If you have clusters of small blisters on the gums or the roof of your mouth (the hard palate), that could be an intraoral herpes outbreak, especially if it’s accompanied by the tingling or burning sensation that cold sores are known for. The treatments below focus on herpes-related cold sores.
Why Timing Matters More Than Anything
Cold sores progress through predictable stages: a tingling or burning sensation (the prodrome), followed by swelling and blister formation, then the blisters break open and crust over into a scab. The whole process takes 5 to 15 days from first tingle to full healing. Blisters typically rupture and begin scabbing within about 48 hours of appearing.
Treatment works best when you start during the prodrome, that early tingling phase that lasts several hours to a day before blisters form. In clinical trials, starting antiviral medication at the first tingle shortened outbreaks by roughly one day compared to placebo. That might not sound dramatic, but it can mean the difference between a blister that fully develops and one that barely surfaces. Once blisters have formed and crusted over, antivirals have much less impact.
Prescription Antiviral Medication
Oral antiviral medication is the most effective treatment for cold sores. The standard prescription regimen is a one-day course: two doses taken 12 hours apart, started at the earliest sign of tingling, itching, or burning. Clinical trials found that this single day of treatment was just as effective as a two-day course, making it a straightforward option you can keep on hand for future outbreaks.
If you get cold sores frequently (six or more times a year), your doctor may recommend taking a lower daily dose continuously as prevention. This suppressive approach reduces both the frequency and severity of outbreaks over time.
Over-the-Counter Cream
The main nonprescription option is a 10% docosanol cream, sold under the brand name Abreva. It works by blocking the virus from entering healthy skin cells, which slows the outbreak’s spread. In a large clinical trial of over 700 patients, docosanol shortened healing time by about 18 hours compared to placebo, with a median healing time of 4.1 days.
That’s a modest improvement, but it’s the only FDA-approved topical treatment available without a prescription. You apply it five times a day at the first sign of a cold sore and continue until it heals. For sores located inside the mouth on the gums or palate, topical creams are harder to keep in place. Gently blot the area dry with gauze before applying, pat the medication on lightly rather than rubbing, and avoid eating or drinking for at least 30 to 45 minutes afterward. Applying a dose right before bed helps because saliva flow drops while you sleep, keeping the medication in contact with the sore longer.
Supplements and Dietary Approaches
Lysine is the most studied supplement for cold sores. It works through a simple competition: lysine and arginine (another amino acid) fight for absorption into your cells, and the herpes virus needs arginine to replicate. By tipping the balance toward lysine, you may limit the virus’s ability to reproduce. Research suggests that doses under 1 gram per day are ineffective, while 3 to 5 grams daily may reduce outbreak severity and improve symptoms during active flares.
On the flip side, foods high in arginine (nuts, seeds, chocolate, and some grains) may encourage outbreaks in people who are prone to them. Some people find that reducing these foods during the tingling stage or supplementing with lysine between outbreaks helps space them out. The evidence is not as strong as it is for prescription antivirals, but the risk of trying is low.
Zinc has also shown some promise. In one small study, patients taking zinc supplements daily for four months cut their number of herpes outbreaks in half over the course of a year, dropping from about six episodes to three.
Light Therapy Devices
A newer option involves handheld devices that deliver near-infrared light directly to the sore. Two randomized controlled trials found that using a specific 1072-nanometer light device for three minutes, three times daily for two days reduced healing time by 48 to 72 hours compared to placebo. In one trial, the treatment group healed in an average of 6.3 days versus 9.4 days for placebo. Patients also reported less pain and burning. These devices are available for home use without a prescription, though they cost more upfront than creams or supplements.
What to Do During an Active Outbreak
While waiting for a cold sore to heal, a few practical steps reduce discomfort and prevent the outbreak from getting worse. Keep the area clean and dry. Avoid touching, picking at, or peeling the scab, which delays healing and increases the risk of bacterial infection. Use a clean finger or cotton swab to apply any topical treatment rather than double-dipping into a tube.
Cold sores are highly contagious from the moment you feel the tingle until the scab falls off completely. Avoid kissing, sharing utensils or cups, and oral contact during this window. If the sore is inside your mouth on the gums or palate, be aware that saliva can transmit the virus.
Over-the-counter pain relievers can take the edge off if the sore is particularly painful. Ice applied to the area for a few minutes at a time may also help with swelling during the early blister stage. For intraoral sores, rinsing with warm salt water several times a day can soothe irritation and keep the area clean.
Signs of a Bacterial Infection
Cold sores occasionally develop a secondary bacterial infection, especially if the blisters are broken open by picking or rubbing. Watch for increasing redness spreading beyond the sore, pus replacing the clear fluid in the blisters, or fever. These signs mean bacteria have moved in on top of the viral infection, and you’ll need antibiotics to clear it. This is uncommon, but worth knowing about so you can act quickly if it happens.