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A mouth ulcer ( aphtha), or sometimes called a canker sore or salt blister, is an ulcer that occurs on the mucous membrane of the oral cavity. Mouth ulcers are very common, occurring in association with many diseases and by many different mechanisms, but usually there is no serious underlying cause. Rarely, a mouth ulcer that does not heal may be a sign of oral cancer. These ulcers may form individually or multiple ulcers may appear at once (i.e., a "crop" of ulcers). Once formed, an ulcer may be maintained by inflammation and/or secondary infection.
The two most common causes of oral ulceration are local trauma (e.g. rubbing from a sharp edge on a broken filling or braces, biting one's lip, etc.) and aphthous stomatitis ("canker sores"), a condition characterized by the recurrent formation of oral ulcers for largely unknown reasons. Mouth ulcers often cause pain and discomfort and may alter the person's choice of food while healing occurs (e.g. avoiding acidic, sugary, salty or spicy foods and beverages).
An ulcer is a tissue defect which has penetrated the epithelial-connective tissue border, with its base at a deep level in the submucosa, or even within muscle or periosteum. An ulcer is a deeper breach of epithelium compared to an erosion or excoriation, and involves damage to both epithelium and lamina propria.
An erosion is a superficial breach of the epithelium, with little damage to the underlying lamina propria. A mucosal erosion is an erosion which specifically occurs on a mucous membrane. Only the superficial epithelial cells of the epidermis or of the mucosa are lost, and the lesion can reach the depth of the basement membrane. Erosions heal without scar formation.
Excoriation is a term sometimes used to describe a breach of the epithelium which is deeper than an erosion but shallower than an ulcer. This type of lesion is tangential to the rete pegs and shows punctiform (small pinhead spots) bleeding, caused by exposed capillary loops.Manfred Strassburg, Gerdt Knolle; translated by Hannelore Taschini Loevy (1993). 9780867152104, Quintessence Pub. Co.. ISBN 9780867152104
Simple mechanisms which predispose the mouth to trauma and ulceration are xerostomia (dry mouth – as saliva usually lubricates the mucous membrane and controls bacterial levels) and epithelial atrophy (thinning, e.g., after radiotherapy), making the lining more fragile and easily breached.Anne Field, Lesley Longman in collaboration with William R. Tyldesley (2025). 9780192631473, Oxford University Press. ISBN 9780192631473 Stomatitis is a general term meaning inflammation within the mouth, and often may be associated with ulceration.
Pathologically, the mouth represents a transition between the gastrointestinal tract and the skin, meaning that many gastrointestinal and cutaneous conditions can involve the mouth. Some conditions usually associated with the whole gastrointestinal tract may present only in the mouth, e.g., orofacial granulomatosis/oral Crohn's disease.
Similarly, cutaneous (skin) conditions can also involve the mouth and sometimes only the mouth, sparing the skin. The different environmental conditions (saliva, thinner mucosa, trauma from teeth and food) mean that some cutaneous disorders which produce characteristic lesions on the skin produce only nonspecific lesions in the mouth. The vesicles and bullae of blistering mucocutaneous disorders progress quickly to ulceration in the mouth, because of moisture and trauma from food and teeth. The high bacterial load in the mouth means that ulcers may become secondarily infected. Cytotoxic drugs administered during chemotherapy target cells with fast turnovers such as malignant cells. However, the epithelia of the mouth also has a high turnover rate and makes oral ulceration (mucositis) a common side effect of chemotherapy.
Erosions, which involve the epithelial layer, are red in appearance since the underlying lamina propria shows through. When the full thickness of the epithelium is penetrated (ulceration), the lesion becomes covered with a exudate and takes on a yellow-grey color. Because an ulcer is a breach of the normal lining, when seen in cross section, the lesion is a crater. A "halo" may be present, which is a reddening of the surrounding mucosa and is caused by inflammation. There may also be edema (swelling) around the ulcer. Chronic trauma may produce an ulcer with a keratosis (white, thickened mucosa) margin. Malignant lesions may ulcerate either because the tumor infiltrates the mucosa from adjacent tissues, or because the lesion originates within the mucosa itself, and the disorganized growth leads to a break in the normal architecture of the lining tissues. Repeat episodes of mouth ulcers can be indicative of an immunodeficiency, signaling low levels of immunoglobulin in the oral mucous membranes. Chemotherapy, HIV, and mononucleosis are all causes of immunodeficiency/immunosuppression with which oral ulcers may become a common manifestation. Autoimmunity is also a cause of oral ulceration. Mucous membrane pemphigoid, an autoimmune reaction to the epithelial basement membrane, causes desquamation/ulceration of the oral mucosa. Numerous aphthous ulcers could be indicative of an inflammatory autoimmune disease called Behçet's disease. This can later involve skin lesions and uveitis in the eyes. Vitamin C deficiency may lead to scurvy which impairs wound healing, which can contribute to ulcer formation. For a detailed discussion of the pathophysiology of aphthous stomatitis, see Aphthous stomatitis#Causes.
An ulcer that keeps forming on the same site and then healing may be caused by a nearby sharp surface, and ulcers that heal and then recur at different sites are likely to be recurrent aphthous stomatitis (RAS). Malignant ulcers are likely to be single in number, and conversely, multiple ulcers are very unlikely to be oral cancer. The size of the ulcers may be helpful in distinguishing the types of RAS, as can the location (minor RAS mainly occurs on non-keratinizing mucosa, major RAS occurs anywhere in the mouth or oropharynx). Induration, contact bleeding and rolled margins are features of a malignant ulcer. There may be nearby causative factor, e.g. a broken tooth with a sharp edge that is traumatizing the tissues. Otherwise, the person may be asked about problems elsewhere, e.g. ulceration of the genital mucous membranes, eye lesions or digestive problems, swollen glands in neck (lymphadenopathy) or a general unwell feeling.
The diagnosis comes mostly from the history and examination, but the following special investigations may be involved: blood tests (vitamin deficiency, anemia, leukemia, Epstein-Barr virus, HIV infection, diabetes) microbiological swabs (infection), or urinalysis (diabetes). A biopsy (minor procedure to cut out a small sample of the ulcer to look at under a microscope) with or without immunofluorescence may be required, to rule out cancer, but also if a systemic disease is suspected. Ulcers caused by local trauma are painful to touch and sore. They usually have an irregular border with erythematous margins and the base is yellow. As healing progresses, a keratotic (thickened, white mucosa) halo may occur.
Aphthous stomatitis and local trauma are very common causes of oral ulceration; the many other possible causes are all rare in comparison.
Eating hard foods (e.g., potato chips) can damage the lining of the mouth. Some people cause damage inside their mouths themselves, either through an absentminded habit or as a type of deliberate self-harm (factitious ulceration). Examples include biting the cheek, tongue, or lips, or rubbing a fingernail, pen, or toothpick inside the mouth. Tearing (and subsequent ulceration) of the upper labial frenum may be a sign of child abuse (non-accidental injury).
Iatrogenic ulceration can also occur during dental treatment, where incidental abrasions to the soft tissues of the mouth are common. Some dentists apply a protective layer of petroleum jelly to the lips before carrying out dental work to minimize this.
The lingual frenum is also vulnerable to ulceration by repeated friction during Cunnilingus ("cunnilingus tongue"). Rarely, infants can ulcerate the tongue or lower lip with the teeth, termed Riga-Fede disease.
Electrical burns in the mouth are usually caused by chewing on live electrical wiring (an act that is relatively common among young children). Saliva acts as a conducting medium and an electrical arc flows between the electrical source and the tissues, causing extreme heat and possible tissue destruction.
Other caustic medications include eugenol and chlorpromazine. Hydrogen peroxide, used to treat gum disease, is also capable of causing epithelial necrosis at concentrations of 1–3%. Silver nitrate, sometimes used for pain relief from aphthous ulceration, acts as a chemical cauterant and destroys nerve endings, but the mucosal damage is increased. Phenol is used during dental treatment as a cavity sterilizing agent and cauterizing material, and it is also present in some over-the-counter agents intended to treat aphthous ulcerations. Mucosal necrosis has been reported to occur with concentrations of 0.5%. Other materials used in endodontics are also caustic, which is part of the reason why use of a Dental dam is now recommended.
The exact cause of aphthous stomatitis is unknown, but there may be a genetic predisposition in some people. Other possible causes include hematinic deficiency (folate, vitamin B, iron), stopping smoking, stress, menstruation, trauma, food allergy or hypersensitivity to sodium lauryl sulphate (found in many brands of toothpaste). Aphthous stomatitis has no clinically detectable signs or symptoms outside the mouth, but the recurrent ulceration can cause much discomfort to those affected. Treatment is aimed at reducing the pain and swelling and speeding healing, and may involve systemic or topical , (pain killers), , anti-inflammatories or barrier pastes to protect the raw area(s).
| + Infectious causes of oral ulceration |
| Example(s) |
| chickenpox, hand, foot and mouth disease, herpangina, herpetic stomatitis, human immunodeficiency virus, infectious mononucleosis |
| acute necrotizing ulcerative gingivitis, gangrenous stomatitis, syphilis, tuberculosis |
| blastomycosis, cryptococcosis, histoplasmosis, paracoccidioidomycosis |
| leishmaniasis |
Opportunistic activity by combinations of otherwise normal bacterial flora, such as aerobic streptococci, Neisseria, Actinomyces, spirochetes, and Bacteroides species can prolong the ulcerative process. Fungal causes include Coccidioides immitis (valley fever), Cryptococcus neoformans (cryptococcosis), and Blastomyces dermatitidis ("North American Blastomycosis"). Entamoeba histolytica, a parasite , is sometimes known to cause mouth ulcers through formation of cysts. Epstein-Barr virus-positive mucocutaneous ulcer is a rare form of the Epstein-Barr virus-associated lymphoproliferative diseases in which infiltrating, Epstein-Barr virus (i.e. EBV)-infected B cells cause solitary, well-circumscribed ulcers in and skin.
Common sites of oral cancer are the lower lip, the floor of the mouth, and the sides, underside of the tongue and mandibular alveolar ridge, but it is possible to have a tumor anywhere in the mouth. Appearances vary greatly, but a typical malignant ulcer would be a persistent, expanding lesion that is totally red (erythroplasia) or speckled red and white (erythroleukoplakia). Malignant lesions also typically feel induration (hardened) and attached to adjacent structures, with "rolled" margins or a punched out appearance and bleeds easily on gentle manipulation. If someone has an unexplained mouth ulcer persisting for more than 3 weeks this may indicate a need for a referral from the GDP or GP to hospital to exclude oral cancer.
The conditions eosinophilic ulcer and necrotizing sialometaplasia may present as oral ulceration.
Macroglossia, an abnormally large tongue, can be associated with ulceration if the tongue protrudes constantly from the mouth. Caliber persistent artery describes a common vascular anomaly where a main arterial branch extends into superficial submucosal tissues without a reduction of diameter. This commonly occurs in elderly people on the lip and may be associated with ulceration.
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