A rare disorder involving inflammation and progressive fibrosis of tissues inside the mouth. The condition starts with redness, blistering and ulceration inside the mouth that is eventually replaced with stiff fibrous tissue as it heals. The inside of the mouth can become stiff and hinder oral functions such as eating, speaking and even opening the mouth. Even the pharynx may occasionally be involved. The condition can become cancerous. The disorder is often associated with chewing betel nuts in Asian and Indian areas. See also Oral submucous fibrosis