Oral sub mucous fibrosis (OSMF) is a chronic condition that affects the oral mucosa, causing stiffness and thickening of the soft tissues in the mouth.

It is commonly seen in individuals who chew or consume areca nut (betel quid) or tobacco products. The exact cause of OSMF is not fully understood, but it is believed to be related to the toxic effects of these substances on the connective tissue in the mouth.

Symptoms of OSMF include difficulty in opening the mouth wide, pain on chewing, and a burning sensation in the mouth.  The condition can also lead to dental problems, such as tooth decay and gum disease, due to poor oral hygiene caused by restricted mouth opening.

The diagnosis of OSMF is based on clinical examination and history of exposure to areca nut or tobacco products. Treatment for OSMF involves quitting the use of these substances and managing symptoms with medications, such as corticosteroids and mucolytic, to reduce inflammation and loosen the tightened tissues.  In severe cases, surgical intervention may be necessary to release the tightened tissues and improve mouth opening.  Prevention of OSMF involves avoiding the use of areca nut and tobacco products altogether.