H. pylori are stomach bacteria that have been linked to stomach ulcers and to gastritis. In the past, it was believed that stress and spicy foods could cause an ulceration of the stomach lining. However, it has been proven that H. pylori are the cause and that ulcers can be successfully treated with antibiotics. Approximately half of people have H. pylori bacteria in their stomach, which were probably picked up during their childhood. Most are asymptomatic. When symptoms of an ulcer present itself, a person can be tested and treated for H. pylori bacteria.