Mouth Ulcer Medicine: Which to Use, How Often, How Many Days to Heal, and How a Dermatologist Tells Canker Sores Apart from Herpes, Hand-Foot-Mouth Disease, and Ulcers That Need Urgent Checking
The mouth ulcers Thai people call "heat ulcers" are usually aphthous ulcers (recurrent aphthous stomatitis), which are shallow, round or oval sores with a white-yellow base and a red border. They hurt a lot when eating or talking and heal on their own within 7–14 days. The most widely used medicine for mouth ulcers is triamcinolone acetonide 0.1% oral paste, which reduces inflammation and pain and helps the ulcer heal about 1–3 days sooner, but it does not make the ulcer disappear right away.
More important than choosing a brand is knowing whether your mouth sore really is a canker sore. Ulcers caused by the herpes virus, hand-foot-mouth disease, fungal infection, or possibly oral cancer can look similar, and a steroid applied to the mouth may make some of these conditions worse. This article explains each group of mouth ulcer medicines, their strengths, how to use them, how long they take to work, how to tell the different ulcers apart, and the signs that mean you should see a doctor.
What are mouth ulcers (canker sores)?
A canker sore, or aphthous ulcer, is a sore on the lining of the mouth that is not caused by infection, is not contagious, and is not caused by "heat in the body" as commonly believed. The current understanding is that the local immune system overreacts to the mouth lining, causing small patches of the lining to die and form an ulcer.
They are very common: about 20% of people have had one. They often start in childhood or the teenage years and can come and go for many years. Typical features are:
Location: the non-keratinized lining, meaning the inside of the lips, inner cheeks, under the tongue, the edges of the tongue, and the floor of the mouth. They rarely appear on the gums attached to the teeth or on the hard palate.
Appearance: a round or oval sore with a white or grey-yellow base surrounded by a red border.
Warning sensation: many people feel burning, stinging, or tingling at the spot 1–2 days before the sore appears.
Healing time: small ulcers heal in 7–14 days without scarring.
How many groups of mouth ulcer medicine are there, and how do you choose?
Topical and local treatments for mouth ulcers fall into 5 main groups, each with a different goal.
Steroids applied to the mouth reduce inflammation so the ulcer shrinks and heals faster. This is the main group for treating canker sores.
Local anesthetics reduce pain temporarily for 15–60 minutes so you can eat, but they do not make the ulcer heal faster.
Antiseptic mouthwashes reduce bacteria that aggravate the ulcer, especially when there are several ulcers or brushing is difficult.
Anti-inflammatory rinses or sprays reduce pain and swelling throughout the mouth.
Protective coating gels form a protective layer so the ulcer is shielded from food and teeth.
For an ordinary canker sore with just 1–3 ulcers, a steroid applied to the mouth is usually enough. If it hurts a lot, a local anesthetic may be added before meals. For several ulcers at once, large ulcers, or very frequent ulcers, a doctor may consider a steroid mouthwash or oral medicine.
How to use triamcinolone 0.1% oral paste effectively
Triamcinolone acetonide 0.1% in oral paste is the most commonly used medicine. The paste is designed to stick to moist mouth tissue for longer than an ordinary cream.
The correct way to use it
Wash your hands, then use a cotton swab or tissue to blot the ulcer dry first, because the medicine sticks better to a dry sore.
Squeeze out a small amount, about the size of a mung bean or roughly 0.5 cm long, and dab it onto the ulcer as a thin film.
Dab gently, do not rub. If you rub, the medicine crumbles into grains and comes off the sore.
Apply 2–4 times a day, after meals and before bed. The bedtime dose matters most because the medicine stays on the ulcer the longest.
After applying, do not drink or eat for 30 minutes.
How long to use it: use it until the ulcer has healed and no longer hurts, generally 5–7 days. If there is no improvement at all after 7 full days, see a doctor, and do not use it continuously for more than 2 weeks without being examined.
How well it works: this medicine reduces pain and helps the ulcer heal about 1–3 days sooner. It works best when you start at the burning stage or on the first day you see the ulcer. If you start when the ulcer is already about to heal by itself, the benefit is small.
Contraindications and precautions
Do not use it on ulcers caused by the herpes virus or by fungus, because a steroid suppresses local immunity and lets the infection spread more.
Using it continuously for several weeks may cause a secondary fungal infection in the mouth, seen as white patches that wipe off.
In young children, pregnant women, and people taking immunosuppressive drugs, talk to a doctor before using it.
Stronger steroids, such as fluocinonide 0.05% gel or clobetasol propionate 0.05%, are used for large ulcers or ulcers that do not respond, and must be used only as prescribed by a doctor.
What can anesthetic gels for mouth ulcers do, and who should not use them?
Local anesthetics let you eat and brush your teeth during the most painful days, but they do not treat the ulcer.
Lidocaine 2% gel or viscous lidocaine: apply to or hold on the ulcer 5–10 minutes before meals. It works for about 30–60 minutes. Do not swallow large amounts.
Benzocaine 10–20% gel: acts quickly, but must not be used in children under 2 years old because of the risk of methemoglobinemia, which causes bluish lips and nails and shortness of breath and can be dangerous.
A precaution for every anesthetic: when the tongue and mouth are numb, you may bite the ulcer or choke on food, especially in children and older adults.
Mouthwashes and sprays for mouth ulcers
Chlorhexidine gluconate 0.12%: rinse with 15 mL for 30 seconds, twice a day, for no more than 2 weeks. It helps reduce repeat infection and makes the ulcer heal slightly faster. Side effects are brown staining of the teeth and tongue, which can be polished off, and a temporary change in taste. Wait 30 minutes after brushing, because the foaming agent in toothpaste inactivates the medicine.
Benzydamine hydrochloride 0.15%: an anti-inflammatory and pain-relieving mouthwash or spray. Use as directed on the label for no more than 7 days. It may sting the first time.
Dexamethasone elixir 0.5 mg/5 mL: used when there are so many ulcers that applying paste to each is impractical. Hold 5 mL in the mouth for 2 minutes and spit it out, 2–4 times a day. Use only as prescribed by a doctor.
Salt water: rinsing with warm salt water (half a teaspoon of salt in 1 glass of water) helps keep the mouth clean and is safe at any age, but it does not make the ulcer heal significantly faster.
Protective coating gels such as hyaluronic acid 0.2% gel or other ulcer-coating gels act like a dressing for mouth sores and reduce friction. They can be used together with a steroid and suit people who wear braces or have ulcers where teeth often rub.
Minor aphthous ulcer (the most common)
Appearance: round or oval ulcers smaller than 1 cm, mostly 3–5 mm, 1–5 at a time, on the inside of the lips, inner cheeks, tongue edges, or under the tongue. They make up about 80% of all canker sores.
Cause: an overactive local immune response, usually with a trigger such as biting the cheek, hard brushing, stress, lack of sleep, menstruation, or very spicy or sour food.
Severity/urgency: not dangerous. Pain is worst in the first 3–4 days, then the ulcer heals on its own within 7–14 days with no scar.
When to see a doctor: the ulcer does not heal within 2 weeks, you get them more than 3–4 times a year, or the pain is so bad you cannot eat or drink.
Major aphthous ulcer: deep and slow to heal
Appearance: deep ulcers larger than 1 cm with raised edges and severe pain. They may appear on the soft palate, the back of the mouth, or near the tonsils, making swallowing painful. About 10–15% of cases.
Cause: the same mechanism as the minor type but more severe. More common in people with iron or vitamin deficiency, people with weakened immunity such as HIV infection, and Behçet's disease.
Severity/urgency: takes 2–6 weeks to heal and may leave a scar in the mouth. Ordinary mouth medicines are usually not enough.
When to see a doctor: see a doctor the first time it happens to confirm it is not another disease. A doctor may use a strong steroid, inject a steroid at the base of the ulcer, or give a short course of oral medicine.
Herpetiform ulcers (clusters of tiny ulcers)
Appearance: very small ulcers of 1–3 mm, 10–100 at once, which may merge into a large ulcer with irregular edges. Pain is felt throughout the mouth. About 5–10% of cases, usually in adult women.
Cause: although the name sounds like herpes, it is not caused by the herpes virus. It is a type of aphthous ulcer.
Severity/urgency: heals in 7–14 days but often returns frequently. Applying medicine is hard because the ulcers are scattered.
When to see a doctor: when there are many ulcers at once, so that herpes infection can be clearly ruled out. A doctor usually uses a steroid mouth rinse, and some patients are given doxycycline in a dissolvable form to rinse with.
Ulcers from biting, brushing, or braces (traumatic ulcer)
Appearance: a single ulcer with an irregular shape at a spot that gets rubbed, such as the tongue edge next to a sharp tooth, the inner cheek along the molars, or where braces wires and brackets sit.
Cause: repeated injury to the same spot, such as a chipped tooth, loose denture, braces wire, biting the cheek while chewing, or hard food cutting the lining.
Severity/urgency: once the cause is removed, the ulcer should heal in 7–10 days. A protective coating gel or orthodontic wax can help.
When to see a doctor: if the ulcer has not healed within 2 weeks after fixing the cause, see a dentist or doctor to have it checked, because a chronic ulcer from friction is one risk factor for oral cancer.
How do herpes sores in the mouth differ from canker sores?
Appearance: starts as small clusters of clear fluid-filled blisters that then break into several shallow ulcers on the outer lips, gums, and hard palate, where canker sores rarely appear. In a child with a first infection, the gums may be red and swollen throughout the mouth, with a fever of 38–39 degrees, drooling, and refusal to eat.
Cause: herpes simplex virus (type 1), spread through saliva and contact. Read more at Cold sores on the lips: causes, how many days to heal, and which medicine works.
Severity/urgency: in adults who have had it before it usually heals within 7–10 days, but young children are at risk of dehydration. Do not apply a steroid to herpes sores. Treatment is an antiviral such as acyclovir or valacyclovir, which works best when started within the first 48–72 hours.
When to see a doctor: a child with fever and sores throughout the mouth who cannot eat or drink, sores near the eye, or a person with weakened immunity.
Mouth ulcers from hand-foot-mouth disease and herpangina
Appearance: several small ulcers at the back of the mouth, the soft palate, and the uvula, together with blisters or a red rash on the palms, soles, and buttocks, and fever. In herpangina, there are sores in the throat without a rash on the hands and feet.
Cause: enteroviruses such as coxsackievirus, common in children under 5 years old, spreading in schools and nurseries during the rainy season.
Severity/urgency: mostly heals on its own within 7–10 days. Treat the symptoms with fever medicine and enough fluids. For more on telling them apart, see Hand, foot and mouth disease: causes and how to tell it from herpes and chickenpox.
When to see a doctor immediately: a child who is drowsy, has a fever for more than 2 days, vomits often, has trembling or jerking hands, or breathes fast, which may be signs of brain and heart complications.
Recurrent mouth ulcers with genital sores or eye inflammation (Behçet's disease)
Appearance: mouth ulcers that look just like canker sores but come back at least 3 times a year, together with genital sores, red or blurred eyes, painful pus bumps or red lumps on the skin, or joint inflammation.
Cause: Behçet's disease, an immune-mediated inflammation of the blood vessels that appears in early adulthood.
Severity/urgency: if the eyes are inflamed it can cause blindness, so it needs treatment by a doctor. Commonly used medicines are colchicine and other immune-modulating drugs. Read more at Behçet's disease: chronic mouth ulcers and treatment.
When to see a doctor: immediately when recurrent mouth ulcers come with genital sores or eye symptoms.
Mouth ulcers that could be oral cancer
Appearance: a single ulcer that is painless or only mildly painful, with a hard raised edge and a firm base when felt, possibly with a white or red patch around it, and bleeding easily. Most often seen on the side of the tongue and the floor of the mouth under the tongue.
Cause/risk factors: smoking, chewing betel, regular alcohol use, sharp teeth or dentures rubbing chronically, infection with certain HPV types, and age 40 or older.
Severity/urgency: a condition that needs early diagnosis, because the earlier it is found the better the treatment works. Do not keep applying a steroid indefinitely, because it makes the ulcer look better for a while and delays diagnosis.
When to see a doctor: any ulcer that has not healed within 2–3 weeks. See a dentist, oral surgeon, or dermatologist for an examination and biopsy.
Mouth sores or patches from other skin diseases
Many skin diseases can occur on the lining of the mouth and are often mistaken for chronic canker sores.
Oral lichen planus: white lacy lines on both inner cheeks. Some types form red painful sores that burn when eating spicy food. Long-term follow-up is needed. See Oral lichen planus: which white patches in the mouth carry a cancer risk.
Pemphigus vulgaris: raw erosions in the mouth that do not heal for months, often appearing before skin blisters. A biopsy is needed. See Pemphigus: an autoimmune blistering disease.
Oral candidiasis: milk-curd-like white patches that wipe off, with red skin underneath. Common in people who use steroid sprays or ointments for a long time, older adults with dentures, and people with diabetes. Treated with an antifungal, not a steroid.
Severe drug rash (SJS/TEN): several mouth ulcers with crusted bleeding lips, red eyes, and a body rash, 1–4 weeks after starting a new medicine. This is an emergency.
Sores at the corners of the mouth are not canker sores but angular cheilitis. See Angular cheilitis: causes and treating it according to the cause.
Mouth ulcers by location: tongue, under the tongue, inner cheek, throat
On the tongue and tongue edges: very painful because the tongue moves constantly. Often caused by biting the tongue or a sharp tooth. Medicine is hard to make stick, so apply it before bed. A hard ulcer on the tongue edge that does not heal within 2 weeks must be examined.
Under the tongue and floor of the mouth: a common site for canker sores, but also a high-risk site for oral cancer, so a chronic ulcer should not be left alone.
Inner cheeks and inside the lips: the most common sites, and easy to apply medicine to.
In the throat, soft palate, tonsils: a single large ulcer may be a major aphthous ulcer. If there are several ulcers with fever in a child, think of herpangina or hand-foot-mouth disease. Use a spray or rinse instead of dabbing.
Gums and hard palate: canker sores rarely appear here. If there are several sores on the gums, think of herpes first.
What causes mouth ulcers, and which vitamin deficiency causes them?
Evidence-based triggers for canker sores include:
Minor injury: biting, hard brushing, hard food, braces.
Stress and not enough rest.
Hormones: some people get them before their period.
Nutritional deficiency: iron, vitamin B12, folic acid, and zinc, found in about 5–20% of people with recurrent canker sores.
Certain foods: chocolate, coffee, nuts, citrus fruit, and very spicy food, in some people.
Toothpaste containing the foaming agent sodium lauryl sulfate: some studies found that switching to a toothpaste without it reduced the number of ulcers in some people.
Medical conditions: celiac disease, chronic inflammatory bowel disease, Behçet's disease, HIV infection.
Certain medicines: NSAID anti-inflammatory drugs, methotrexate, nicorandil.
Quitting smoking: some people get canker sores more often in the first period after quitting, which is not a reason to go back to smoking.
As for the idea that "eating fried or oily food, longan, or durian causes heat ulcers", this is a folk belief that has no clear medical evidence.
Frequent mouth ulcers: what to test, and are there pills?
If you get canker sores more than 3–4 times a year, or are almost never ulcer-free, a doctor usually looks first for correctable causes:
Blood tests: a complete blood count (CBC), stored iron (ferritin), vitamin B12, and folate.
Further tests depending on symptoms: celiac disease antibodies if there is chronic diarrhea or weight loss, an HIV test if there is risk, and an eye examination if Behçet's disease is suspected.
Treatment to reduce how often they come back
Replace what is lacking: iron, vitamin B12, or folate supplements according to the blood results. Most people need 2–3 months before the ulcers become less frequent. One study found that sublingual vitamin B12 1,000 micrograms once a day reduced ulcers even when blood levels were normal.
Colchicine 0.5 mg once or twice a day: used in people with very frequent ulcers or large ulcers. It must be taken continuously for at least 1–3 months before judging the result. The most common side effect is diarrhea.
Short course of oral steroid for 5–7 days (prednisolone): used only during periods with several large ulcers. The doctor sets the dose by body weight. It is not used routinely.
Other medicines in severe cases: such as other immune-modulating drugs, which must be under specialist care.
Signs that treatment is working are fewer episodes per month, smaller ulcers, and faster healing. The choice of medicine and dose is the doctor's decision after an examination.
How to make a mouth ulcer heal faster: self-care at home
Start applying medicine as soon as you feel burning or on the first day you see the ulcer.
Blot the ulcer dry before each application, and always apply before bed.
Avoid very spicy, very sour, very salty, hard crunchy foods, and very hot drinks while you have an ulcer.
Choose a soft toothbrush, brush gently, and try a toothpaste without foaming agents.
Drink enough water and eat soft cool foods such as warm porridge and yogurt.
You can take paracetamol for pain according to the label dose if the pain is bad.
If you wear braces, use orthodontic wax over the wire where it cuts.
Do not dab the ulcer with alcohol, skin antiseptic, rock salt, or caustic substances, because they kill more tissue and make the ulcer bigger.
Mouth ulcers in children and pregnant women: what can be used?
Children
Several mouth ulcers with fever in a young child are mostly a viral infection, such as first-time herpes or hand-foot-mouth disease, not a canker sore. Have a doctor examine the child before using any medicine on the mouth.
Do not use benzocaine in children under 2 years old.
Triamcinolone oral paste can be used in older children in small amounts as advised by a doctor.
Watch for dehydration, such as passing less urine, a dry mouth, or drowsiness.
Pregnant and breastfeeding women
Canker sores may occur more often because of hormonal changes.
Salt water, protective coating gels, and small amounts of topical lidocaine can usually be used.
A small amount of oral steroid paste for a short time is generally considered safe, but always talk to a doctor or pharmacist first.
Which mouth ulcers are dangerous and need a doctor?
An ulcer that has not healed within 2–3 weeks
An ulcer larger than 1 cm, or with a hard edge, or a firm lump felt under it
A painless ulcer that looks large, or a white or red patch that cannot be wiped off
Ulcers more often than 3–4 times a year, or a new ulcer appearing before the old one has healed
Fever, weight loss, or hard enlarged lymph nodes in the neck
Genital sores, red or blurred eyes, or a body rash along with the ulcer
An ulcer that appeared after starting a new medicine
Being unable to swallow or drink, especially in children and older adults
Preparing for the doctor visit: take photos of the ulcer on day 1 and day 7, note how many times you had them in the past year and how many days each lasted, all the medicines you are taking, and any other symptoms that came with it.
In brief
Most mouth ulcers are aphthous ulcers. They are not contagious, and a small ulcer heals on its own within 7–14 days.
The main medicine is triamcinolone 0.1% oral paste: blot the ulcer dry, dab without rubbing, 2–4 times a day, and no more than 7 days if there is no improvement.
Anesthetics reduce pain temporarily but do not speed healing. Do not use benzocaine in children under 2 years old.
Do not apply a steroid to ulcers from herpes, fungus, or hand-foot-mouth disease. You have to tell them apart first.
If you get them more than 3–4 times a year, get blood tests for iron, B12, and folate deficiency.
An ulcer that does not heal in 2–3 weeks, has a hard edge, or is painless needs a doctor's examination.
Frequently asked questions about mouth ulcer medicine and canker sores
What medicine do you use for a mouth ulcer?
For an ordinary canker sore, the most commonly used medicine is triamcinolone acetonide 0.1% oral paste. Apply a thin layer on the ulcer after blotting it dry, 2–4 times a day after meals and before bed, with lidocaine anesthetic before meals if it hurts a lot, and a 0.12% chlorhexidine rinse if there are several ulcers. But if the sore is a cluster of blisters on the lips or gums, it may be herpes, which needs an antiviral instead, and a steroid must not be used. The right choice for each person should be assessed by a doctor or pharmacist.
How do you make a mouth ulcer heal fast?
Start the oral steroid paste as soon as you feel burning or on the first day you see the ulcer. Blot the ulcer dry before applying, dab the medicine on gently without rubbing, and apply every night before bed. Avoid spicy, sour, hot, and hard crunchy food, and use a soft brush and a toothpaste without foaming agents. These measures help the ulcer heal about 1–3 days sooner and hurt less. However, nothing makes an ulcer heal in a single day, and dabbing alcohol or salt on it will make it bigger.
How many days does a mouth ulcer take to heal?
The minor aphthous ulcer, the most common type, heals on its own within 7–14 days, with the worst pain in the first 3–4 days. Herpetiform ulcers also heal in 7–14 days. A major aphthous ulcer, larger than 1 cm, may take 2–6 weeks and leave a scar. If any ulcer has not healed within 2–3 weeks, whatever its size, see a doctor or dentist for an examination, because it may not be a canker sore.
How many types of canker sore are there?
Canker sores come in 3 types. The first is the minor type, up to 1 cm, 1–5 at a time, making up about 80% of cases and healing in 7–14 days. The second is the major type, over 1 cm, deep and very painful, healing in 2–6 weeks and possibly scarring. The third is the herpetiform type, 1–3 millimeters and dozens at a time, which is not caused by the herpes virus. There are also mouth ulcers from other causes that look similar, such as ulcers from biting, herpes, and hand-foot-mouth disease.
Which vitamin deficiency causes mouth ulcers?
Some people with frequent recurring canker sores are deficient in iron, vitamin B12, folic acid, or zinc, found in about 5–20% of people with recurrences. But most people who get canker sores are not vitamin deficient, so taking multivitamins without testing may not help. If you get them more than 3–4 times a year, have blood tests for a complete blood count, ferritin, vitamin B12, and folate, then replace what is lacking, which usually takes 2–3 months before the ulcers become less frequent.
Which mouth ulcers are dangerous?
Mouth ulcers that need to be seen by a doctor soon include an ulcer that has not healed within 2–3 weeks, an ulcer with a hard edge or a firm lump felt under it, a painless ulcer that looks large, an ulcer with a white or red patch that cannot be wiped off, an ulcer with enlarged neck lymph nodes or weight loss, an ulcer with genital sores or eye inflammation, or several ulcers after starting a new medicine. People who smoke, chew betel, or drink alcohol regularly should be especially wary of chronic ulcers on the tongue edge and under the tongue, because these are high-risk sites for oral cancer.
The information in this article is general knowledge to help you decide whether to see a doctor. It is not a diagnosis or a personal prescription. The choice of medicine, dose, and duration of use is the doctor's decision after an examination.
Read about other skin diseases and mucosal conditions written by our dermatologists at the Skin Conditions article hub.
Written by Dr. Patara Voravutinon, Dermatologist · Last reviewed October 6, 2026
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