Yes, COVID-19 can cause sores in the mouth. A meta-analysis in Frontiers in Medicine found that roughly one in three hospitalized COVID patients developed some form of oral lesion, with about 10% specifically developing ulcers resembling canker sores. These sores aren’t listed among the most well-known COVID symptoms, but they’re far from rare, and researchers believe many are directly caused by the virus rather than being a coincidence.
Why COVID Affects the Mouth
The virus that causes COVID-19 enters your cells by latching onto a specific protein found on cell surfaces called ACE2. Your mouth is rich in this protein, particularly in the cells lining your tongue, cheeks, and gums, as well as in your salivary glands. Once the virus gets into these oral tissues, it triggers an inflammatory response that can damage the delicate lining of your mouth, leading to sores, ulcers, and other visible changes.
Beyond direct viral invasion, the inflammation can also affect tiny blood vessels in your mouth, causing problems with blood flow that lead to tissue damage, small areas of bleeding under the surface, and even localized tissue death in severe cases. This combination of direct cell damage and vascular inflammation explains why COVID-related mouth sores can look so different from person to person.
Types of Mouth Sores Linked to COVID
COVID doesn’t produce just one kind of mouth sore. The range of oral changes reported in patients is surprisingly wide:
- Canker sore-like ulcers: The most commonly reported type. These are painful, round or oval sores with a reddish border, typically appearing on the inner cheeks, lips, or tongue. They generally heal within 5 to 15 days.
- Herpetiform lesions: Clusters of small, painful, yellowish-gray ulcers with red borders. These look similar to herpes outbreaks but test negative for the herpes virus.
- Erythema multiforme-like lesions: Red, target-shaped patches that can blister and ulcerate, often appearing on the lips and inside the cheeks.
- White plaques and coatings: Whitish patches on the tongue or inner cheeks, sometimes caused by fungal overgrowth triggered by immune suppression.
- Tongue changes: Red, bald-looking patches where the tiny bumps on the tongue surface have flattened, sometimes with swelling and indentations along the edges.
A Spanish hospital study of 666 COVID-positive patients found that among those with oral involvement, the breakdown included inflamed tongue bumps (11.5%), tongue inflammation with bite-mark indentations (6.6%), canker sore-like ulcers (6.9%), patchy smooth areas on the tongue (3.9%), and general mouth inflammation (3.9%).
What “COVID Tongue” Looks Like
One of the more distinctive oral signs is what’s been called “COVID tongue.” It typically presents as red, smooth patches of varying size on the tongue surface, surrounded by an irregular white border. The appearance is similar to geographic tongue, a harmless condition where the surface pattern shifts over time. But in COVID patients, these changes are often accompanied by a burning sensation, dry mouth, and altered taste. The patches may change shape and size over the course of days.
When Mouth Sores Appear and How Long They Last
The timing varies considerably. Mouth sores can show up anywhere from 4 days before other COVID symptoms to as late as 12 weeks after. Most commonly, ulcers and erosions appear about 4 to 7 days into the illness. Erythema multiforme-like lesions tend to show up later, between 7 and 24 days after systemic symptoms begin.
Healing times also depend on the type of sore. Simple canker sore-like ulcers typically clear up in 5 to 15 days. More complex ulcers and erosions can take 5 to 21 days. The target-shaped lesions generally need 2 to 4 weeks to fully resolve. In many cases, mouth sores heal around the same time as the overall COVID infection resolves.
Dry Mouth Makes It Worse
Dry mouth is extremely common during COVID, with studies reporting it in 30% to over 98% of patients depending on the population studied. The virus can directly damage salivary glands through those same ACE2 receptors, and many medications used to treat COVID symptoms also reduce saliva production.
This matters because saliva is your mouth’s primary defense system. It washes away bacteria, neutralizes acids, and keeps the soft tissue moist and resilient. When saliva production drops, your mouth becomes more vulnerable to ulcers, fungal infections, and bacterial overgrowth. If you’re dealing with COVID and notice your mouth feels unusually dry, staying well-hydrated and using sugar-free lozenges to stimulate saliva can help protect the tissue.
Secondary Infections: Thrush and Fungal Overgrowth
Not all mouth sores during COVID are caused by the virus itself. COVID suppresses certain immune functions, and treatments like corticosteroids and broad-spectrum antibiotics further shift the balance in your mouth, allowing fungi that normally live there in small numbers to overgrow. In one study of 544 hospitalized COVID patients, about 3.6% developed oral thrush, a fungal infection that appears as creamy white patches that can be wiped away to reveal raw, red tissue underneath.
Thrush during COVID is worth paying attention to because it requires different treatment than viral sores. If you notice white patches that scrape off, or a cottony feeling in your mouth during or after a COVID infection, that’s more likely a fungal issue than a direct viral effect.
How to Tell COVID Sores From Regular Canker Sores
This is genuinely difficult, even for clinicians. COVID-related ulcers can look nearly identical to ordinary canker sores. A few patterns can help you sort it out. Timing is the biggest clue: if mouth sores appear alongside or shortly after other COVID symptoms like fever, fatigue, or loss of taste and smell, the connection is likely. Ordinary canker sores tend to follow stress, minor injuries (like biting your cheek), or hormonal changes, not respiratory infections.
Location offers some hints too. COVID-related herpetiform lesions can appear on both keratinized tissue (like the hard palate and gums) and non-keratinized tissue (like the inner cheeks and lips), while regular canker sores almost always stick to non-keratinized surfaces. If you’re seeing clusters of small ulcers on your gums or hard palate during a COVID infection, that pattern is more characteristic of a viral cause. COVID mouth sores also tend to come in multiples and may be accompanied by tongue changes, dry mouth, and altered taste, a constellation you wouldn’t expect from a simple canker sore.
Managing Mouth Sores During COVID
Most COVID-related mouth sores resolve on their own as the infection clears. In the meantime, the goal is comfort and preventing secondary complications. Keeping your mouth clean with gentle saltwater rinses (half a teaspoon of salt in a cup of warm water) several times a day helps reduce bacterial load without irritating damaged tissue. Avoiding spicy, acidic, or very hot foods and drinks will spare you unnecessary pain.
Over-the-counter oral pain gels containing numbing agents can provide temporary relief for particularly painful ulcers. If dryness is a major issue, sipping water frequently, using alcohol-free mouthwash, and running a humidifier at night can help. For sores that persist beyond three weeks or are severe enough to interfere with eating and drinking, a dentist or doctor can evaluate whether a topical prescription treatment or antifungal is needed.