The immune system has evolved to protect individuals from microbial pathogens as well as larger parasites. However, the immune system can sometimes react inappropriately to innocuous antigens, triggering allergic reactions. The potential of microorganisms, microbial products and enzymes to induce respiratory sensitization when used as food and feed additives was investigated in this report. A short review of the state-of-the-art methods to predict allergenicity was also conducted. Our results indicate that there is currently no established model to predict the allergenicity of a molecule. Although in-silico models can be useful to predict cross-reactivity between allergens, they do not take into account phenomenons like the context of presentation of the antigen to the immune system. There is no realiable, predictive in-vitro or in-vivo model of allergenicity. Cases of occupational allergy to both fungi and bacteria have been documented, but allergic reactions to microorganisms purposedly introduced in the work environement seem to concern only a limited number of fungi. Enzymes were more a matter of concern, with 17 out of 71 enzymes investigated in this report being linked to respiratory allergies. Because these risks are well known, enzyme exposures are strictly controlled both by regulatory authorities and companies. The patterns of prevalence of allergic reactions to enzyme indicate that they are more common at the level of enzyme manufacturers and large-scale users than in the general population.