H. pylori infection is the biggest risk factor for gastritis. Though it may occur in half the world's population, it is most common in developing countries. Mostly there are no symptoms of the infection. If you take aspirin regularly, you risk developing gastritis. This is also true if you're on anti-inflammatory pain relievers for a chronic condition. Use of aspirin and other NSAIDs for a long time can cause stomach irritation and bleeding. Another risk is age; older people are at higher risk of gastritis because their stomach lining gets thinner with age and because they are more likely to have H. pylori infection or autoimmune disorders.
Attribution: Avallain