COVID Mouth Sores: Why They Happen and What to Do

COVID-19 can directly and indirectly cause a range of mouth sores, from painful ulcers and blisters to white patches and inflamed gums. A large systematic review covering thousands of patients found that oral ulceration affected about 8% of people with confirmed infections, while broader oral symptoms like dry mouth and taste changes were even more common.¹ The reasons these sores develop are more varied than most people realize, involving everything from the virus attacking oral tissue directly to medications triggering secondary infections.

How the Virus Gets Into Oral Tissue

SARS-CoV-2 enters cells by latching onto a protein called ACE2, which acts like a doorway on cell surfaces. The mouth happens to be rich in ACE2, particularly on the tongue, the inner lining of the cheeks, and the gums. Research using tissue staining has confirmed that ACE2-positive cells in the mouth sit mainly in the outer epithelial layers, right where the virus would make first contact.² A second protein called furin, which the virus also exploits for cell entry, shows up in the same locations. This means the lining of your mouth is not just a passive bystander during infection; it is an active site where the virus can replicate and cause direct tissue damage.

Once the virus takes hold in oral tissue, the immune system’s inflammatory response compounds the problem. Elevated levels of inflammatory signaling molecules in COVID-19 patients can disrupt the normal balance of tissue repair in the mouth, leading to delayed healing and a greater chance that small injuries turn into full-blown sores.³ So the mouth sores are not simply the virus eating away at tissue. They are also the result of the body’s own defense system overshooting.

What These Sores Actually Look Like

There is no single “COVID mouth sore.” The lesions that show up in infected patients span a wide range, including ulcers, erosions, blisters, white or red patches, and areas where the tongue loses its normal texture.⁴ In one systematic review, the single most commonly reported lesion was oral ulceration, appearing in up to 47% of cases in individual studies. Tongue changes, including a swollen or patchy-looking tongue, came in next, followed by gum inflammation and hemorrhagic lesions.⁵

The tongue is the most frequently affected site overall, involved in roughly a quarter of patients with oral symptoms, followed by the general oral mucosa, the lips, the gums, and the palate.¹ Some patients develop just one type of lesion, but many end up with several at once, which is part of what makes the experience so miserable. Pain, sensitivity to touch, and difficulty eating and drinking are common complaints. In one reported case, the lesions were severe enough to interfere with speaking.⁶

COVID Tongue

One of the more distinctive oral findings associated with COVID-19 earned its own informal name. “COVID tongue” refers to a pattern of patchy depapillation, meaning areas on the tongue surface where the tiny bumps (papillae) flatten out or disappear, giving the tongue a smooth, sometimes map-like appearance. It resembles geographic tongue, a harmless condition that predates the pandemic, but researchers noted it occurring at a higher-than-expected rate in people with active infections.⁷ In one field hospital study, glossitis with patchy depapillation was found in about 4% of hospitalized COVID patients.

Beyond the visual changes, COVID tongue can come with a burning sensation, dry mouth, and altered taste. Case reports describe patients whose tongue surfaces appeared swollen and reddened alongside these texture changes.⁸ While COVID tongue sounds alarming, it tends to be self-limiting, meaning it resolves on its own as the infection clears. Still, it can persist for weeks in some cases, particularly when it overlaps with other oral symptoms.

When Dormant Viruses Wake Up

Not every mouth sore during a COVID infection is caused by SARS-CoV-2 itself. One underappreciated mechanism is the reactivation of herpes viruses that already live dormant in the body. Most adults carry herpes simplex virus type 1 (the cold sore virus), and many also carry varicella-zoster virus (the chickenpox/shingles virus). These viruses hide quietly in nerve tissue and can flare up whenever the immune system is preoccupied or suppressed.

COVID-19 appears to create exactly those conditions. A cross-sectional study found that the prevalence of both HSV-1 and varicella-zoster was significantly higher in COVID patients compared to controls, even after adjusting for other health conditions like diabetes and obesity.⁹ Researchers have speculated that COVID lowers the threshold for reactivation of these common viruses, and severe COVID with acute respiratory distress has been flagged as a particular risk factor for herpes family reactivation.¹⁰

This matters practically because herpes-driven mouth sores look and feel different from other COVID oral lesions. They typically appear as clusters of small blisters that rupture into shallow, painful ulcers, often on the lips or hard palate. If you develop this pattern during or shortly after a COVID infection, it is worth mentioning to your doctor, because antiviral treatment for herpes (like acyclovir) works well when started early and is a different approach than managing inflammation-driven ulcers.

Thrush and Other Opportunistic Infections

Oral candidiasis, commonly known as thrush, is another frequent hitchhiker during COVID-19. The white, cottage-cheese-like patches on the tongue and inner cheeks that characterize thrush are caused by an overgrowth of Candida yeast, which normally lives in the mouth in small amounts. COVID creates a perfect storm for Candida: the immune system is diverted to fighting the virus, antibiotics used for suspected secondary bacterial infections wipe out competing bacteria, and corticosteroids prescribed to tamp down dangerous inflammation further suppress local immune defenses.

In one hospital-based study of 100 COVID patients, 30% developed oropharyngeal candidiasis. Among those with severe COVID, the rate was 45%, compared to 15% in mild cases. Patients who received corticosteroids were especially vulnerable, with 70% of candidiasis patients having been on steroids versus 40% of those without thrush.¹¹ Longer hospital stays also raised the risk. Thrush during COVID is treatable with antifungal medications, but it needs to be recognized for what it is rather than lumped in with other “COVID mouth sores,” because the treatment is entirely different.

Dry Mouth and Salivary Gland Problems

Dry mouth, or xerostomia, is one of the most common oral complaints during COVID, reported by roughly 13% of patients in one large review and up to 44% in observational studies that tracked symptoms closely.¹ ¹² The wide range in reported numbers likely reflects differences in how dry mouth was measured and whether patients were asked about it directly.

The salivary glands express ACE2, making them a target for the virus. A case series found that xerostomia sometimes appeared before the more recognized symptoms like fever and cough, raising the possibility that dry mouth could serve as an early warning sign of infection.¹³ Beyond the direct viral effect on salivary glands, mouth breathing due to nasal congestion, dehydration from fever, and side effects of medications like antihistamines all contribute.

Dry mouth is not just uncomfortable. Saliva plays a critical protective role, washing away bacteria and keeping the oral lining moist. When saliva production drops, the mouth becomes more vulnerable to ulcers, thrush, and gum problems, so xerostomia can actually set the stage for other oral complications.

Severity Matters

Oral lesions during COVID are not distributed randomly. They track with how sick a person gets. Older adults and people with more severe infections tend to develop more widespread and painful mouth sores.¹⁴ A study analyzing oral hygiene and COVID outcomes found a statistically significant association between disease severity and the number of oral lesions, with more lesions on the tongue and cheek lining as the disease worsened from mild to severe.¹⁵

Poor oral hygiene before and during the infection also appears to be an aggravating factor. People who are hospitalized or quarantined and unable to maintain their normal dental care routines may be at higher risk for developing oral complications. This is a practical point worth remembering: keeping up with brushing and rinsing during a COVID illness, even when you feel terrible, can reduce the chance of secondary oral problems.

Children and Multisystem Inflammatory Syndrome

Kids with COVID tend to have milder respiratory symptoms than adults, but they are not immune to oral manifestations. A review of 47 pediatric patients with multisystem inflammatory syndrome in children (MIS-C), a rare but serious complication of COVID, found that nearly half had red or swollen lips and about 11% had a strawberry tongue, a bright red tongue with enlarged bumps.¹⁶ These oral findings overlapped significantly with skin rash and eye inflammation, suggesting they are part of a systemic inflammatory response rather than a local infection in the mouth.

The oral signs of MIS-C resemble those of Kawasaki disease, a condition that was already known to cause cracked lips, strawberry tongue, and oral mucosal redness in children. A systematic review confirmed that across both MIS-C and Kawasaki-like presentations linked to COVID, the most common oral changes were swollen or cracked lips, erythematous (red) oral mucosa, oral ulcers, and strawberry tongue.¹⁷ These signs in a child who has recently had COVID or been exposed should prompt medical evaluation, since MIS-C requires specific treatment.

Mouth Sores That Persist After Recovery

For some people, oral symptoms do not clear up when the acute infection ends. In a survey-based study of long COVID patients, about 46% reported mouth sores, 48% reported dry mouth, and 58% had lingering changes in taste or smell.¹⁸ Healthcare professionals who saw these patients most frequently observed oral thrush, xerostomia, COVID tongue, recurrent ulcers, and gum infections.

An observational study tracking patients through recovery found that while many oral symptoms decreased in frequency after the acute phase, burning sensation and recurrent mouth ulcers actually increased during recovery.¹² A related meta-analysis of COVID-related burning mouth syndrome found that symptoms like mouth ulcers and gum bleeding persisted in a subset of patients well after the infection had resolved.¹⁹ The salivary glands may also be affected long-term, with emerging reports of persistent salivary gland problems as a feature of long COVID.²⁰

If you are dealing with mouth sores weeks or months after a COVID infection, you are not imagining things. The evidence suggests this is a recognized pattern. Bringing it up with a dentist or primary care doctor is worthwhile, because some of these conditions, like recurrent thrush or persistent xerostomia, have specific treatments that can help.

What You Can Do About COVID Mouth Sores

Treatment depends entirely on what type of oral problem you are dealing with, which is why getting a proper look from a healthcare provider matters. The general management strategies reported across studies fall into a few categories:

Ulcers and erosions: Topical analgesic gels, medicated mouthwashes (often containing a corticosteroid component), and avoiding spicy or acidic foods that aggravate the sores. A case report described a patient whose COVID-related oral lesions improved by about 90% after a month of mouth rinse therapy, though the sores recurred periodically over six months before fully resolving.²¹
Thrush: Antifungal medications, either topical (like nystatin rinse) or systemic (like fluconazole) for more stubborn cases. If you are on corticosteroids for COVID, rinsing your mouth after each dose can help prevent thrush from developing in the first place.
Herpes reactivation: Antiviral drugs like acyclovir or valacyclovir, ideally started within the first couple of days of blister onset for the best effect.
Dry mouth: Frequent sips of water, sugar-free lozenges or gum to stimulate saliva, saliva substitutes, and avoiding alcohol-based mouthwashes that can worsen dryness.

For children, the approach scales with severity, ranging from simple pain relief with topical gels to systemic medications when a condition like MIS-C is involved.²² The key point is that “COVID mouth sores” is not a single condition with a single fix. Ulcers, thrush, herpes blisters, and dry mouth each call for a different approach, and treating one as though it were another can leave you frustrated and unhealed.

Can COVID Vaccines Cause Mouth Ulcers?

Mouth ulcers have also been reported as a side effect of COVID mRNA vaccines, though the incidence is low. An analysis of Japan’s adverse drug event database found 204 reported cases of mouth ulcers associated with COVID mRNA vaccines out of tens of millions of doses administered. The signal was statistically significant, with a reported odds ratio of 1.6 compared to other drugs in the database. About three-quarters of those affected were women, and the median time to symptom onset was two days after vaccination.²³

Most cases resolved on their own, but a small percentage, around 11-12%, were classified as unrecovered at the time of reporting. For context, no unrecovered cases were found with influenza vaccines in the same database. Vaccine-related mouth ulcers are worth being aware of, but the overall numbers are small relative to the hundreds of millions of doses given worldwide. If ulcers appear a day or two after your shot and do not clear up within a couple of weeks, it is reasonable to mention it at your next medical visit.

The Mouth as a Window Into Infection

Beyond being a site of symptoms, the mouth has turned out to be a surprisingly useful sampling site for detecting and monitoring SARS-CoV-2 itself. Saliva carries measurable viral loads, and research has shown that testing saliva with sensitive assays could detect infection up to four and a half days before viral loads in nasal swabs reached detectable levels using standard tests.²⁴ Viral RNA has been found in over 90% of saliva samples from confirmed COVID patients, including people without symptoms, and higher salivary viral loads have been linked to worse clinical outcomes.²⁵

This has practical implications. The presence of virus in saliva reinforces why oral symptoms show up so frequently during COVID and why the mouth may serve as both an entry point and a reservoir for the virus. It also helps explain why oral lesions tend to be more common and more severe in patients with higher overall disease burden: there is simply more virus present in the tissue.

Erythema Multiforme and Look-Alikes

One clinical challenge with COVID mouth sores is distinguishing them from drug reactions. Erythema multiforme, a condition that causes target-shaped skin lesions and painful oral erosions, can be triggered by both the virus itself and by medications used to treat COVID. Researchers have proposed splitting COVID-associated erythema multiforme into three patterns: a virus-related form in younger patients (under 30), a virus-related form in older patients (over 55), and a drug-induced form, most often linked to hydroxychloroquine. Telling these apart in a patient who is simultaneously fighting a viral infection and taking multiple medications is genuinely difficult, even for specialists.²⁶

The practical takeaway is that if you develop widespread, painful mouth sores during or shortly after COVID, especially if they are accompanied by a skin rash, it is worth getting a proper evaluation rather than assuming they will just go away. Some of these conditions resolve on their own, but others benefit from specific treatment, and a few may signal a drug reaction that warrants changing your medication regimen.

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