Bayesian interpretation of the hygiene hypothesis

Abstract

Immunity is crucial for an organism to survive as it prevents intrusions of pathogens and accompanying infections. However, the immune system may react to benign stimulants such as pollens or certain types of foods, which is prevalent in modern societies. This allergic response is the outcome of the hypersensitive response to external substances which can be described as an error of the immunological decision-making. Here, I utilized Bayes’ theorem to interpret one of the main hypotheses of the allergy: the hygiene hypothesis. The probability that the immune system reacts to the benign substances is expected to be determined by the probability to encounter the benign antigen, the probability of an immune response, and the likelihood that the benign antigen elicits the immune response. The statistical analyses show that infrequent exposure to virulent pathogens during childhood may increase allergic responses, supporting the hygiene hypothesis. This interpretation combined with an evolutionary perspective may provide a novel framework for understanding the allergy response.