Aphthous stomatitis caused by a reduction in numbers of CD4+ T cells may be implicated in RAS-type ulceration in HIV infection. The thickness of the mucosa may be an important factor in aphthous stomatitis. Usually, ulcers form on the thinner, non-keratinizing mucosal surfaces in the mouth. Factors which decrease the thickness of the mucosa increase the frequency of occurrence, and factors which increase the thickness of the mucosa correlate with decreased ulceration. The nutritional deficiencies associated with aphthous stomatitis (Vitamin B12, folate, and iron) can all cause a decrease in the thickness of the oral mucosa (atrophy). Local trauma is also associated
Aphthous stomatitis self healing ulcers at fairly regular intervals. Although there are many causes of oral ulceration, "recurrent" oral ulceration has relatively few causes, most commonly aphthous stomatitis, but rarely Behçet's disease, erythema multiforme, ulceration associated with gastrointestinal disease, and recurrent intra-oral herpes simplex infection. A systemic cause is more likely in adults who suddenly develop recurrent oral ulceration with no prior history. Special investigations may be indicated to rule out other causes of oral ulceration. These include blood tests to exclude anemia, deficiencies of iron, folate or vitamin B12 or celiac disease. However, the nutritional deficiencies may be latent and the