The most common causes include Recurrent aphthous stomatitis (RAS) —also called recurrent aphthous ulcers (RAU) Viral infections, particularly herpes simplex and herpes zoster Other infectious agents (Candida albicans and bacteria) Trauma Tobacco or irritating foods or chemicals Chemotherapy and radiation therapy Systemic disorders Table Evaluation of Stomatitis History History of present illness should ascertain the duration of symptoms and whether the patient ever had them previously.