How are Helicobacter and allergy related?

The relationship between Helicobacter pylori (Hp) and allergies is complex and debated. Epidemiological studies often report an inverse association: Hp infection, especially with CagA-positive strains, appears to reduce the risk of asthma, hay fever, and atopic dermatitis. This aligns with the hygiene hypothesis, where early microbial exposure promotes immune tolerance. Hp induces regulatory T cells (Tregs) and may suppress excessive Th2 responses. However, evidence is mixed; some studies find no association or even a positive link, e.g., with allergic rhinitis. Importantly, Hp is a gastric pathogen causing gastritis, ulcers, and gastric cancer. Eradication for allergy prevention is not recommended. Most data come from observational studies; randomized trials are lacking. For consumers: a positive Hp test (stool, breath) does not guarantee allergy protection, and Hp should only be treated if symptomatic. The evidence grade is human-moderate: meta-analyses exist but causality remains uncertain.