Allergology (from the Greek ἄλλος - other, different, alien, ἔργον - impact and Λόγος - knowledge, word, science) is a branch of medicine that studies allergic reactions and diseases, their causes, mechanisms of development and manifestation, methods of their diagnosis, prevention and treatment. Immunology (from Latin immunis - free, liberated, freed from anything + Greek λόγος - knowledge) is a biomedical science that studies the body's reactions to foreign structures (antigens): the mechanisms of these reactions, their manifestations, the course and outcome in norm and pathology, as well as developing methods of research and treatment.