Helicobacter pylori may cause asymptomatic infections, gastritis, ulcer and severe gastric cancers in infected persons and this bacteria was also classified as class I human carcinogen by the IARC. Bacterial factors, host and environmental factors act together in the development of gastric cancer. While Treg responses are particularly observed in infected asymptomatic patients, the dominant development of the immune response towards Th1, together with the host's tendency, provide a basis for the gastric cancer process. Nowadays, together with improved living conditions, immunization policies against infections and moving away from crowded living conditions the prevalence of atopic diseases and asthma are remarkably increasing. According to the hygiene hypothesis; living in hygienic conditions and non-exposure to infectious agents in early years of life, lead to the underdevelopment of Treg response and prevent the development of immunotolerance and consequently relative predominance of Th2 response leading to emergence of allergic diseases. The relationship between H. pylori and gastric cancer was proven by many studies. However, in recent years, several studies have drawn attention to the relation between the presence of H. pylori and protection from allergic diseases. The increase in Treg response in H. pylori-infected individuals was reported to be related to protection from asthma. In this review; H. pylori was evaluated in terms of gastric cancer development and protection from allergic diseases and asthma. Although there is a lot of research about the relation between H. pylori and gastric cancer, further studies investigating its role in prevention from allergic diseases are needed to find an answer to the question “Could H. pylori be a beneficial microorganism?”. We believe that in the near future an increasing number of studies will try to find the answer to the question ‘'In addition to the known harmful aspects of H. pylori, is it also a beneficial agent?''