What Is Mouth Sore?

The oral cavity or our mouth is a dynamic environment made up of different types of tissues. Given this high variation in its anatomy and physiology (normal functioning), our mouths can be sore for multiple reasons such as dryness, inflammation, thinning of the skin (mucosa) inside it, or, more commonly, erosions and ulcerations inside the mouth.1

Erosions are commonly referred to wider sores affecting only the superficial layers of the skin lining the mouth. Ulcers are referred to as sores where the superficial skin (epithelium) and the connective tissue (lamina propria) underneath it are both involved.1 Ulcers are one of the most common causes of sore mouths worldwide.1,2 There are many varied causes of mouth ulcers, but some common causes of mouth ulcers or sores include immunological disorders (gastrointestinal disorders, skin disorders, aphthous stomatitis, etc.), blood disorders (anaemia, vitamin B12 deficiency etc.), infections, cancers, trauma, burns, and drug-related reactions.2

They can form on the tongue, gums, cheeks, lips, floor, and roof of the mouth. They appear generally wound-like, with additional variations based on their underlying causes.2 Some of them such as cold sores may be contagious.1,2 Mouth ulcers are generally not very severe and heal within two weeks without intervention.1,2 They are often quite painful and may affect the quality of life due to pain and achiness.1,2 If they do last longer, it is advisable to visit your dentist as soon as possible to rule out infections or other serious conditions like oral cancers.1,2

Treatment and management commonly include topical creams or agents to reduce symptomatic pain or achiness from the open wound. In severe cases, steroids, immune system modifying agents, or other forms of therapy may also be needed.1,2

Causes of Mouth Ulcers

The causes of mouth ulcers are very varied and thus, dependent on the underlying cause there can be different types of ulceration that can occur in the mouth.

Immunological causes

Aphthous ulcers, or “Canker Sores”

They are recurrent ulcers with a red ring (halo) on the borders of the ulcers.3 Based on their appearance, they are further classified into herpetiform (pin-point ulcers), minor aphthae (larger than herpetiform ulcers, 2-6 ulcers with episodic appearance), major aphthae (>1cm in diameter, may last for over a month, and can heal with scarring).3
They affect about 20-25% of the general population, with a stronger predisposition in assigned females at birth and people under 40.3 Some of the most common associated factors triggering the immune response, in turn causing aphthous ulceration include stress, trauma, food allergies, chemical reactions, sudden smoking cessation, and specific systemic diseases.3

Lichen Planus

Oral lichen planus is an immune disorder that affects the skin inside the mouth. It causes painful ulcers inside the mouth lasting over long periods of time.4 Oral cancer can be a further complication in around 2% of cases of lichen planus with oral ulcers.4

Vesiculobullous disorders

These are autoimmune disorders that commonly cause blistering of the oral mucosa (skin) which eventually burst to leave behind ulcerated areas. Some common vesiculobullous conditions that can cause ulcers include Pemphigus Vulgaris and Mucous Membrane Pemphigoid.1

Other disorders

Following is a list of some other common immunological causes that can also cause ulceration inside the mouth:1

1. Erythema Multiforme

2. Coeliac disease

3. Crohn’s disease

4. Orofacial granulomatosis

5. Chronic ulcerative colitis

6. Granulomatosis with polyangiitis

7. Bechet’s syndrome

8. Lupus erythematosus

This list is not exhaustive and there can be many more underlying immunological causes of mouth ulcers.

Blood disorders

Blood disorders sometimes cause oral ulcers and in most cases are accompanied by other signs and symptoms as well.1 Following are some blood disorders that cause mouth ulcers:1

1. Anaemia

2. Leukaemias

3. Haematinic deficiencies

4. Neutropenia

Infective causes

Infective causes of ulceration can be classified into bacterial, viral, and fungal.1 The ulceration varies based on the underlying microorganism that causes the ulcers. Some of the infections might be highly contagious and often require further treatment.1 Some examples of infective causes of mouth ulcers are:1

1. Bacterial – Acute necrotising gingivitis, syphilis, tuberculosis

2. Viral – Herpes viruses (Cold sores), Hand Foot Mouth viral disease, HIV, infectious mononucleosis (kissing disease)

3. Fungal – Oral thrush, histoplasmosis, blastomycosis

Malignant neoplasms (Cancerous tumours)

One of the leading causes of death worldwide, most oral cancers such as squamous cell carcinoma cause ulceration of the oral mucosa.5 These ulcers are commonly non-healing, feel hard to touch in and around it, are painless, and may also numb the affected area and appear to be growing or spreading.5 Some common causes of Oral Cancers include the consumption of tobacco products, alcohol use, viral infections, and inherited genetic risks.5


Ulcers caused by trauma are mostly isolated ulcers localised to the area of the trauma but in some cases, it may be widespread as well.1 Some traumatic causes that may cause ulceration include:1 (NHS)

1. Accidental biting on the inside of the cheek or lip

2. Poorly fitting dentures, rough fillings, or a sharp tooth

3. Burns caused by hot food or chemical/radiation burns

4. Trauma caused while brushing your teeth

Drug-induced ulceration

Drug-related ulceration appears similar to other ulcers with the exception that they are generally resistant to common treatments for ulcers.6 Some medications that can cause oral ulcerations are:1,6

1. Nicorandil

2. Alendronate

3. Bisphosphonates


Signs and symptoms

Mouth ulcers are normally easy to spot.1

They appear as sores or wound-like areas on different surfaces inside the mouth with white, yellow, or grey-looking centre areas.1-6 The signs and symptoms of ulcers, including the shape, type, number, and frequency typically vary based on underlying causes.1-6  

Some common symptoms that might accompany mouth sores include:

  • Pain in and around the areas where the ulcer might be present
  • Difficulty eating or drinking that is typically increased on consuming salty or spicy foods
  • An increase in soreness or difficulty while brushing your teeth
  • Some inflammation and swelling generally accompany ulcers

Secondary symptoms also vary based on the underlying cause such as fever in cold sores or tuberculosis or increased soreness and redness of the tongue in vitamin B12 deficiencies.1,6


Diagnosis is usually based on history and clinical examination by trained professionals. It typically involves identifying the underlying cause through history taking and by assessing clinical characteristics (number, persistence, shape, and appearance of ulcers) or symptoms accompanying them.1

Your healthcare provider may also physically palpate the ulcer to rule out other causes e.g., malignancies.1 Additionally, an examination of other body areas may also need to be checked for secondary signs to help establish a more definitive diagnosis.1

Moreover, blood tests or other investigations such as microbiological investigations, glucose assays, or imaging scans may also be ordered by your treating physician to aid in diagnosis and treatment.1  

In most cases, biopsy and examination of the tissue sample are also needed to establish a final diagnosis.1

Treatment and Management

Treatment and management of ulcers are divided into symptomatic relief and treating the underlying cause of the ulcer.1 Following are some common approaches to treating and managing mouth sores or ulcers:


Pain relief and discomfort management through self-care are possible through the use of over-the-counter topical creams or coating agents e.g., benzydamine spray and Orajel gel. Maintaining good oral hygiene can be key to promoting faster healing of ulcers. Hence oral hygiene products such as chlorhexidine mouthwash may often help patients.1,7

Medical interventions

Medical interventions in treating oral ulcers are need-dependent and highly individualized.7,8 Following are some frequently used medical interventions to treat oral ulcers:1,7,8

  • Steroid tablets, creams, gels, or inhalers
  • Topical immunosuppressants
  • Systemic immunosuppressants or immune system modifying therapy
  • Over-the-counter nutritional supplements
  • Secondary medication such as antivirals or antibiotics (needed based on the underlying cause)
  • For malignancies – Treatment will require advanced medical intervention such as surgery, radiotherapy, or even chemotherapy
  • Identifying the trigger and eliminating it such as discontinuation or replacement of the medication in drug-induced ulceration

Prevention strategies

In cases where the ulceration or soreness is chronic (present over a long duration) or reoccurs, identifying the underlying triggers is crucial. They might be salty or spicy foods, metal fillings, or sharp dentures. It is essential to avoid them or get their replacements to prevent further relapse. Maintaining good oral hygiene as stated earlier, is an important factor in avoiding oral ulceration, although this may not always be the case.1,7,8

Complications and when to see a dentist/doctor

Some possible complications of mouth ulcers include cancers and secondary/contagious infections.1-8 As discussed above, mouth ulcers are common in the general population and in most cases heal without intervention. But if you notice any of the following signs/symptoms, it is advisable to visit your dentist or GP surgery at the earliest:1-8

  • Non-healing ulcers that last longer than 2 - 3 weeks
  • Increase in the number of ulcers
  • Secondary symptoms like fever or diarrhoea
  • Soreness or ulceration that does not improve with medication
  • Painless, numb or hard-feeling areas in and around the ulcer/mouth
  • Ulcers affecting outer parts of the lips
  • Bleeding or discharge from the ulcer
  • Ulcers keep reoccurring  

Frequently Asked Questions 

How common are mouth sores?

They are the most common cause of soreness in the mouth.1 Recurrent aphthous ulcers or canker sores, the most common type of mouth ulcers, develop in 20-25% of the general population and are more commonly reported in assigned females.1,3

Are mouth sores contagious?

All of them are not contagious but some of them might be, such as cold sores or blistering ulcers on the outer lips caused by viruses are highly contagious sores since the infection can be transmitted through contact with the sore.1-5

How can I manage mouth sores at home?

Symptomatic relief using over-the-counter numbing sprays or creams such as benzydamine or Orajel, may help in managing mouth sores at home.1-8 Additionally maintaining good oral hygiene, eating a healthy and balanced diet, and avoiding triggers are also ways of managing mouth sores at home.1-8


Ulcers are one of the most common causes of sore mouths worldwide.1,2 Some common causes of mouth ulcers or sores include blood disorders, infections, immunological disorders, cancers, trauma, burns, and drug-related reactions.2 They are easy to spot and appear as sores or wound-like with white, yellow or grey-looking centre areas.1 Their appearance, number, and frequency typically vary based on underlying causes.1-6  Accompanying symptoms include pain, discomfort, difficulty eating or drinking (especially salt or spicy foods), and soreness or difficulty while brushing your teeth.1-6 Diagnosis is commonly based on patient history and clinical examination by trained professionals. Additional biopsies, blood tests, or other investigations such as microbiological investigations, glucose assays, or imaging scans may also be needed.1  Treatment and management generally include self-care symptomatic relief using over-the-counter numbing sprays or gels, maintaining good hygiene, and avoiding trigger substances.7,8 Additional medical interventions may include steroids, immune system modifying/suppressing therapy, and any secondary treatment (antivirals and antibiotic medications) as needed based on the underlying cause.1-8 While ulcers are not mostly life-threatening, certain conditions may need timely dental/medical attention.


This content is purely informational and isn’t medical guidance. It shouldn’t replace professional medical counsel. Always consult your physician regarding treatment risks and benefits. See our editorial standards for more details.

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Aumiyo Kumar Das

B.D.S., MSc. Oral Medicine – University of Bristol, United Kingdom

Aumiyo Das is a postgraduate qualified dentist, who has completed his undergraduate dentistry from Nair Hospital Dental College, Mumbai and his Postgraduate MSc in Oral Medicine with distinction from University of Bristol.

He has 5 years of global healthcare experience spanning a variety of clinical and non-clinical roles in different healthcare settings across India, the U.K. and the U.S.A. He has extensive experience working in the pandemic both clinically and in healthcare management.

He has briefly also assisted in the delivery of a course at the Global Health Academy, The University of Edinburgh and has also worked on the delivery of digital health projects globally in small island nations.

He is currently involved in assisting with the delivery of the PG Dip in Digital Health Leadership for the NHS digital academy and other postgraduate digital healthcare leadership and global public health programmes at the Institute of Global Health Innovation at Imperial College London.

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