Why mouth blisters turn into ulcers so quickly, and when one is worrying
The lining of your mouth sits at the border between gut and skin, and it is thinner than either, so the slightest scrape from a broken filling can open a sore. Most mouth ulcers are harmless and heal on their own, but one that lingers past two or three weeks deserves a professional look.
An ulcer is a true crater: the damage breaks through the surface layer of cells into the connective tissue beneath, sometimes reaching muscle or bone lining. Shallower injuries, called erosions, look red because the underlying tissue shows through, and they heal without scars. Once a sore goes deeper it becomes coated in a yellow-grey film of fibrin, often ringed by a reddened halo of inflamed tissue.
By far the two commonest causes are local injury and aphthous stomatitis, better known as canker sores, which recur for reasons that remain largely unknown. Injury comes in many forms: sharp teeth, dentures or braces rubbing the cheek, biting a lip that is still numb after dental anaesthetic, crunchy food such as potato chips, or a hot drink taken before sensation returns. Microwaved food that is cool outside but scalding inside has increased burns on the roof of the mouth. Toddlers who chew live electrical cable can suffer severe burns, because saliva conducts current. Pressing an aspirin against an aching tooth, a common home remedy, can chemically destroy the neighbouring lining.
The mouth's wet, thin, constantly chewed surface also changes how other diseases look. Blisters from skin disorders burst almost immediately and leave ulcers, and conditions of the whole digestive tract, such as a form of Crohn's disease, may show up only in the mouth. Dry mouth or tissue thinned by radiotherapy makes breaks more likely. Many ulcers appearing repeatedly can point to Behçet's disease, and a lack of vitamin C, leading to scurvy, slows healing.
Clinicians weigh how long a sore has lasted, its size, colour, number and whether it feels hard or has a rolled edge. A sore that returns to one spot suggests a nearby sharp surface. Cancerous ulcers are usually single, while crops of many are very unlikely to be cancer; a biopsy settles uncertain cases.
Source: Mouth ulcer
