OBJECTIVE This review examines the relationship between exposure to workplace allergens and the risk of developing occupational allergy. RESULTS Evidence suggests that the risk of developing occupational allergy increases with allergen exposure; however, with some occupational allergens, this exposure-response relationship is more complex. In laboratory animal workers, the risk of developing occupational allergy increases with exposure, except at high allergen exposure when there is a reduction in sensitization. This attenuation of specific immunoglobulin E antibody is associated with increased specific immunoglobulin G4 antibodies, which are likely to play a protective role, leading to a form of natural tolerance. Exposure-response relationships are also very dependent on the genetic susceptibility of the individual. The interaction between genes, occupational allergens and other cofactors in the environment, such as endotoxin, are also important risk factors in the development of sensitization and asthma. CONCLUSIONS Occupational allergy provides a good opportunity to understand the complex relationships between exposure to allergens in the workplace, interaction with genes and the coexposures with other factors in the working environment and the increased risk of developing occupational allergy.