The exact pathogenesis is dependent upon the cause. Ulcers and erosions can be the result of a spectrum of conditions including those causing auto-immune epithelial damage, damage because of an immune defect (e.g., HIV, leukemia, infections e.g. herpes viruses) or nutritional disorders (e.g., vitamin deficiencies). Simple mechanisms which predispose the mouth to trauma and ulceration are xerostomia (dry mouth – as saliva usually lubricates the mucous membrane and controls bacterial levels) and epithelial atrophy (thinning, e.g., after radiotherapy), making the lining more fragile and easily breached. Stomatitis is a general term meaning inflammation within the mouth, and often may be associated with ulceration.