Most mouth sores appear as small round or oval spots that are white or yellow in the center with a red border. But that’s only one type. Mouth sores vary widely depending on their cause, and knowing what yours looks like can help you figure out what you’re dealing with and whether it needs attention.
Canker Sores
Canker sores are the most common type of mouth sore. They show up inside the mouth, on the tongue, inner cheeks, gums, or soft palate. They are not contagious. A typical canker sore is a shallow, round or oval ulcer with a white or yellowish center and a bright red ring around the edge. They hurt, especially when you eat, drink, or talk.
Minor canker sores are less than 1 centimeter across and usually heal within two weeks without scarring. Major canker sores are larger, often 1 to 3 centimeters, with irregular borders. These dig deeper into the tissue, can take up to four weeks to heal, and sometimes leave scars. A third type, called herpetiform canker sores, looks like a cluster of tiny pinpoint ulcers that merge into one larger, raised bump. Despite the name, these aren’t caused by the herpes virus.
Cold Sores
Cold sores look completely different from canker sores. They appear on or around the lips, not inside the mouth, and they go through distinct visual stages over roughly a week.
Before anything is visible, you’ll typically feel tingling, burning, or itching in one spot on your lip. A day or two later, one or more small blisters filled with clear fluid appear on the surface of the skin. The skin around the blisters turns red. Within a few days, those blisters break open into shallow, red, weeping sores. This is the stage when they’re most contagious. After that, the sore dries out and forms a yellow or brown crust that eventually falls off as the skin heals underneath.
Cold sores are caused by the herpes simplex virus and tend to recur in the same spot. If you’ve had one before, you’ll likely recognize the tingling feeling before the blister even appears.
Oral Thrush
Oral thrush has a very distinctive look. It produces creamy white, slightly raised patches on the tongue, inner cheeks, and sometimes on the roof of the mouth, gums, or tonsils. The patches have a soft, lumpy texture, often described as looking like cottage cheese. Unlike other white patches in the mouth, thrush can be wiped or scraped off, leaving behind a red, raw surface that may bleed slightly.
Thrush is a fungal infection and is most common in babies, older adults, people with weakened immune systems, and those using inhaled corticosteroids for asthma. It can also make the corners of your mouth crack and turn red.
Hand, Foot, and Mouth Disease
This viral illness, common in young children but possible in adults, causes mouth sores that start as small red spots on the tongue and the insides of the mouth. Those red spots quickly blister and become painful ulcers. The sores usually appear alongside a skin rash on the palms of the hands and soles of the feet, which is the giveaway that distinguishes this from a simple canker sore outbreak.
Sores From Injury
Biting your cheek, burning your mouth on hot food, or irritation from braces, retainers, or rough dental work can all create ulcers that look a lot like canker sores. These traumatic ulcers are typically white or yellow in the center with a red border. The key difference is location: they show up exactly where the injury happened. A cheek bite creates a sore on the inner cheek right along the bite line. A burn from hot pizza creates an ulcer on the roof of your mouth.
These sores usually heal on their own within one to two weeks once the source of irritation is removed. If a sharp edge on a tooth or appliance keeps rubbing the same spot, the sore may persist or keep coming back until the cause is fixed.
White and Red Patches That Don’t Heal
Not all mouth sores are ulcers or blisters. Some appear as flat patches of changed color, and these deserve closer attention.
Leukoplakia shows up as a white patch or plaque that cannot be scraped off (unlike thrush). The surface can be smooth or wrinkled, and the patch is typically painless. It most often appears on the tongue, floor of the mouth, or inside the cheeks. Leukoplakia itself isn’t cancer, but it’s considered a precancerous change, meaning a small percentage of these patches can become malignant over time.
Erythroplakia is rarer but more concerning. It appears as a fiery red, velvety patch with well-defined borders. The surface may be smooth or slightly granular, and the patch can sit flat or slightly depressed below the surrounding tissue. Erythroplakia carries a higher risk of being or becoming cancerous than white patches do.
Oral Lichen Planus
This chronic condition creates a lacy, web-like pattern of slightly raised white lines on the inside of the cheeks. The lines have a delicate, net-like appearance and are sometimes called Wickham’s striae. In mild cases, the white lines are painless and may go unnoticed. In more severe forms, lichen planus can also produce red, eroded areas or open sores that burn when you eat spicy or acidic food.
When a Mouth Sore May Be Something Serious
Most mouth sores are harmless and heal within two weeks. The warning signs that something more serious may be going on are straightforward: a sore that doesn’t heal after two weeks, a white or red patch that persists, a lump or growth inside the mouth, or a sore that keeps getting bigger instead of better.
Oral cancer can look like a non-healing ulcer, a persistent white or reddish patch, or a lump. It doesn’t always hurt, which is why painlessness alone isn’t reassuring if the sore has been there for a while. Recurring mouth sores can also signal underlying conditions like vitamin deficiencies, celiac disease, Crohn’s disease, lupus, or other autoimmune disorders, especially if the sores appear in clusters or come back frequently without an obvious trigger.
The two-week rule is a useful benchmark. A canker sore or traumatic ulcer that’s healing normally should be noticeably smaller and less painful by the end of the first week, and gone or nearly gone by two weeks. Anything that stalls, grows, or changes in appearance after that point is worth having evaluated.