The ‘hygiene hypothesis’ has been used to justify a belief common among homoeopaths that the suppression of childhood infections and immunisation may lead to the development of chronic atopic diseases. The influence of childhood infections and immunisation on the development of atopy was analysed in a qualitative systematic review of direct epidemiological evidence concerning the influence of childhood infections and immunisation on the development of atopy. The results suggest that childhood infections do not protect against atopy; on the contrary, they increase the risk of allergic diseases. Vaccination was not a risk factor for atopy.