Biological molecules are increasingly becoming part of therapeutic arsenal of dermatologist. This is due to their high safety profile, efficacy, and specificity in relation to key targets of disease pathogenesis. However, due to the complexity of their structure and heterogeneity, such drugs can be recognized by the host’s immune system as foreign. The phenomenon of antidrug antibody formation is not new in dermatology. Doctors who use genetically engineered biological drugs in their practice have an issue with problem of primary or secondary drug inefficiency every day. In most cases, this phenomenon is based on immunogenicity, namely, the ability of biological preparations to provoke a humoral and cellular immune response, leading to the formation of neutralizing antibodies that limit the effectiveness and duration of drug molecule action. A number of factors not only of the drug molecule itself, but also the features of the course of disease, which differ significantly in different patients, is influenced to the process of antibody formation. Knowledge of immunogenicity algorithms will help to successfully apply biological therapy to patients of different profiles.