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. Vesiculobullous diseases
Some of the viral infections mentioned above are also classified as vesiculobullous diseases. Other example vesiculobullous diseases include pemphigus vulgaris, mucous membrane pemphigoid, bullous pemphigoid, dermatitis herpetiformis, linear IgA disease, and epidermolysis bullosa. : 1, 22

Allergy
Rarely, allergic reactions of the mouth and lips may manifest as erosions; however, such reactions usually do not produce frank ulceration. An example of one common allergen is Balsam of Peru. If individuals allergic to this substance have oral exposure they may experience stomatitis and cheilitis (inflammation, rash, or painful erosion of the lips, oropharyngeal mucosa, or angles of their mouth). Balsam of Peru is used in foods and drinks for flavoring, in perfumes and toiletries for fragrance, and in medicine and pharmaceutical items for healing properties. Other causes
A wide range of other diseases may cause mouth ulcers. Hematological causes include anemia, hematinic deficiencies, neutropenia, hypereosinophilic syndrome, leukemia, myelodysplastic syndromes, other white cell dyscrasias, and gammopathies. Gastrointestinal causes include celiac disease, Crohns disease (orofacial granulomatosis), and ulcerative colitis. Dermatological causes include chronic ulcerative stomatitis, erythema multiforme (Stevens-Johnson syndrome), angina bullosa haemorrhagica and lichen planus.
Diagnostic
Diagnosis of mouth ulcers usually consists of a medical history followed by an oral examination as well as examination of any other involved area. The following details may be pertinent: The duration that the lesion has been present, the location, the number of ulcers, the size, the color and whether it is hard to touch, bleeds or has a rolled edge. As a general rule, a mouth ulcer that does not heal within 2 or 3 weeks should be examined by a health care professional who is able to rule out oral cancer (e.g. a dentist, oral physician, oral surgeon, or maxillofacial surgeon). If there have been previous ulcers that have healed, then this again makes cancer unlikely. 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 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.