Gastritis is an inflammation of the mucus membrane that lines the stomach. It can be caused by irritation of the stomach lining by a drug (aspirin or alcohol) or by a bacterial infection of the stomach.
Acute gastritis is characterized by a sudden attack. It may cause erosions in the stomach lining that bleed easily.
Chronic gastritis develops over a longer period. It can result from prolonged irritation of the stomach by alcohol, tobacco smoke, or bile. This may cause blood to continually ooze from the stomach lining.