What are Mouth Sores? Oral Canker Sores, Mouth Ulcers

A mouth sore or canker sore is a shallow and painful ulcer in the mouth cavity (inside of the mouth). Mouth sores are also known as aphthous ulcers and can occur on the sides of the mouth cavity (inside of the cheek), under or on the tongue or inner lip. The condition of multiple, recurring mouth sores is medically referred to as aphthous stomatitis.

The inner lining of the mouth (buccal mucosa) is a thin epithelial layer (mucus membrane)  and is susceptible to damage – infection, irritation and injury. The mouth is teeming with several species of bacteria which can cause secondary infection of  a mouth ulcer and this will prolong the ulceration or aggravate the pain and inflammation. Once formed, mouth ulcers are prone to constant irritation and injury due to the the daily activities associated with the mouth – eating, drinking and talking.

Types of Mouth Sores

Other mouth infections and conditions, like oral candidiasis (oral thrush) to leukoplakia, are often referred to as mouth sores. However a canker sore is a mouth ulcer which is shallow, painful, red and appears ‘raw’.


A mouth sore usually starts off as a tender bump on the mouth lining and eventually this swells and bursts open exposing the deeper tissue to the environment within the mouth cavity. A mouth ulcer or canker sore should not be mistaken with a cold sore which occurs on the outside, particularly on the skin around the mouth or outer lip. Mouth sores may recur frequently, sometimes in clusters or in isolation and can affect talking and eating due to pain and discomfort. The inner lining of the mouth usually heals quite rapidly but due to constant physical  trauma from eating, talking, smoking or medication, the ulcer may not get a chance to heal completely.

A mouth ulcer can be considered as a minor ulcer, less than 1 centimetre in diameter or a major ulcer which is usually greater than 1 centimetre in diameter. Minor ulcers usually resolve within 10 to 14 days while major ulcers may persist for several weeks to months. Effective treatment may reduce the severity and duration of the ulcer, especially in chronic, recurring mouth sores.

Mouth Sores & Immune Functioning

The exact cause of canker sores is unknown although they are more likely to occur in immune deficient individuals (especially in HIV/AIDS sufferers where a fungal infection causes oral thrush), at times of stress or persons suffering with certain autoimmune conditions like Crohn’s disease, ulcerative colitis and systemic lupus erythematosus (SLE). Spicy and acidic foods or  hot and cold drinks may increase pain and discomfort and should be avoided until the ulcers heal.

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