Mouth Sores and Mouth Ulcers: Causes, Treatment and When to See a Dentist

Mouth sores are common, and most are harmless. Almost everyone gets one at some point: a tender spot on the inner cheek, tongue or lip that makes eating, drinking and even talking uncomfortable. Many settle within a week or two, but some keep returning or refuse to heal, and those deserve a closer look. This guide explains what mouth sores are, how mouth ulcers differ from cold sores, what can cause sores inside the mouth, what may help at home and when to see a dentist. It is general information, not a diagnosis.

What Are Mouth Sores?

"Mouth sores" is an everyday term for any ulcer, blister or small lesion on the oral mucosa, the soft, moist lining of the mouth. They can appear on the inner cheeks, tongue, gums, lips, roof of the mouth or floor of the mouth. A mouth ulcer is an open sore with a defined edge, while "oral lesion" is the broader clinical term for any abnormal change in the mouth's tissue. Because different conditions can look alike, a sore's appearance alone does not show its cause.

Common Types of Mouth Sores

Canker Sores (Aphthous Ulcers)

Aphthous ulcers, often called canker sores, are the most common mouth ulcers. They are round or oval with a white or yellow centre and a red border, and usually form on the softer lining of the inner cheeks, lips, tongue or floor of the mouth. Minor aphthous ulcers are small and typically heal within one to two weeks. Major aphthous ulcers are larger, deeper and more painful, and can take longer to heal. Aphthous ulcers are not contagious.

Cold Sores

Cold sores are caused by the herpes simplex virus. They often begin with tingling or itching, then form fluid-filled blisters on or around the lips that crust over. Occasionally they appear on the gums or roof of the mouth. Unlike aphthous ulcers, cold sores are contagious, especially while blistered, so avoid kissing and sharing cups, cutlery or towels until they have healed.

Traumatic Mouth Ulcers

Traumatic ulcers form where the mouth has been injured, for example by an accidental cheek bite, a hot-food burn, rough brushing, a sharp tooth or a dental appliance that rubs. They usually heal once the irritation is removed, but a repeated source of trauma can keep the ulcer going.

Persistent Oral Sores

A persistent oral ulcer is one that has not healed after about two weeks. Most have a harmless explanation, but a sore that does not heal, or appears with a lump, a red or white patch, numbness or unexplained bleeding, should be examined to establish the cause.

What Causes Mouth Sores?

Causes differ between individuals, and many sores have no single identifiable trigger. Commonly associated factors include:

• Physical irritation: cheek or tongue biting, sharp tooth edges, rough fillings, and ill-fitting dentures or braces.

• Stress and hormonal changes: some people notice recurring mouth ulcers during stressful periods or hormonal shifts.

• Nutritional factors: low iron, vitamin B12 or folate are associated with recurrent ulcers, but most mouth ulcers are not caused by deficiencies. A doctor can arrange testing.

• Viral infections: herpes simplex causes cold sores, and other viral illnesses can cause sores inside the mouth.

• Medications: some medicines can cause mouth ulcers as a side effect. Do not stop prescribed medication without medical advice.

• Underlying medical conditions: some digestive and immune conditions are linked with recurring ulcers, so frequent or severe sores warrant a medical review.

Common Symptoms of Mouth Sores

Symptoms depend on the type of sore. Typical features are pain or tenderness, redness and inflammation around the sore, a white or yellow centre, and difficulty eating or drinking. Some people have a single ulcer, while others get multiple or recurring ulcers, and some sores simply do not heal.

Not every sore in the mouth is an ulcer. Red, swollen gums that bleed can point to gum disease, so see our guide to spotting gingivitis, and a pimple-like swelling on the gum can be a sign of a tooth abscess, which needs prompt dental attention.

How to Treat Mouth Sores

Treatment depends on the type, location, severity, duration and suspected cause of the sore. Most minor ulcers settle on their own, so care focuses on comfort and protecting the area while it heals. A pharmacist can suggest topical gels, rinses or protective pastes, though some are unsuitable for children or people with certain conditions. If a sharp tooth, rough filling or rubbing appliance is the cause, a dentist can smooth, adjust or repair it. Cold sores may be managed with antiviral products suggested by a pharmacist or doctor. Prescription medicines are only appropriate after a clinical assessment, and no single treatment works for every sore.

Home Remedies That May Help Relieve Mouth Sores

•  Rinse gently with warm salt water (about half a teaspoon of salt in a glass of warm water) and spit it out.

•  Brush with a soft toothbrush, taking care around the sore, and keep the rest of your mouth clean.

• Avoid spicy, salty, acidic and crunchy foods while the sore is tender, and choose cool, soft foods and plain water.

•  If mouthwash stings, choose an alcohol-free one.

Do not apply aspirin, concentrated essential oils or other irritating substances directly to an ulcer, as they can burn the tissue and make healing harder. These measures may ease discomfort, but they are not guaranteed to speed healing.

When Should You See a Dentist for Mouth Sores?

An ulcer that lasts more than about two weeks should be assessed by a dentist or doctor, particularly if it is unexplained or not healing. Arrange an assessment with a general dentist if a sore:

•     keeps returning or appears in clusters

•     is unusually large, growing or very painful

•     appears with a lump, a red or white patch, numbness or bleeding

•     has no obvious cause, or began after a new medicine or denture

Most persistent sores are not serious, and finding the cause early gives the most options. Seek urgent medical care for difficulty swallowing or breathing, swelling of the face, tongue or throat, a high fever with widespread sores, or an inability to drink fluids. Call 111 in an emergency, or Healthline on 0800 611 116 for free health advice. For severe pain or swelling, our emergency dental care experts explains how to contact a clinic.

How Can You Help Prevent Mouth Sores?

Not every sore is preventable, but a few habits help. Brush gently with a soft brush (see choosing a toothbrush), note any foods or products that seem to trigger sores, and eat a balanced diet. Have sharp teeth, rough fillings or rubbing dentures checked, and keep up regular check-ups and a professional dental hygiene clean, which help spot sources of irritation early.

Frequently Asked Questions

How long do mouth sores usually last?

Minor aphthous ulcers usually heal within one to two weeks, and cold sores often clear in a similar time. Major ulcers can take longer. A sore that has not healed after about two weeks should be assessed.

What is the difference between a mouth ulcer and a cold sore?

A mouth ulcer is an open sore, usually inside the mouth, and typical aphthous ulcers are not contagious. A cold sore is caused by the herpes simplex virus, usually forms blisters on or around the lips, and is contagious.

Can stress cause mouth ulcers?

Stress is associated with outbreaks in some people, but it is not the cause for everyone. Injury, nutritional factors, medications and underlying conditions can also play a part.

Are mouth sores contagious?

Typical aphthous ulcers and traumatic ulcers are not contagious. Cold sores are, and some viral illnesses that cause mouth sores can spread, so wash hands and avoid sharing cups or cutlery.

What helps relieve mouth sore pain?

Warm salt-water rinses, soft and cool foods, avoiding spicy or acidic foods, and a pharmacist-recommended topical product may ease discomfort. See a dentist or doctor if the pain is severe or not improving.

When should a mouth sore be checked by a dentist?

Have it checked if it lasts around two weeks, keeps returning, is getting worse, has no clear cause, or comes with a lump, a patch, numbness or bleeding.

Get Professional Advice for Persistent Mouth Sores in Auckland

If a sore has not healed after about two weeks, keeps returning or you are unsure what is causing it, a dental examination is a sensible next step. Auckland Family Dental has five clinics, in Milford, Parnell, Drury, New Lynn and Southern Care Dental, and you can book an appointment at the one nearest you. If a medical cause is suspected, your dentist may suggest seeing your doctor. This article is general information and does not replace professional advice.