Summary: Adverse reactions to foods represent an increasingly common clinical problem; however, not all symptoms reported by patients are immunologically mediated. In clinical practice, the term “food allergy” is often overused, which – together with the growing availability of laboratory tests – contributes to overdiagnosis of food allergy and unjustified dietary restrictions. The aim of this article is to discuss current principles of diagnosing food allergy and food intolerance and to highlight the correct interpretation of diagnostic test results in relation to the clinical presentation. Food allergy is defined as a reproducible clinical reaction with an immunological basis, which may occur through IgE- -mediated, non-IgE-mediated, or mixed mechanisms, whereas food intolerances do not involve immunological pathways and are usually dose dependent. The cornerstone of diagnosing IgE-mediated food allergy is a detailed clinical history combined with targeted diagnostic testing, including skin prick tests and measurements of food-specific IgE antibodies. These tests confirm sensitization but do not, by themselves, establish the diagnosis of clinically relevant food allergy. Component-resolved diagnostics may support differentiation between primary sensitization and cross-reactivity and assist in assessing the risk of systemic reactions, but their results must also be interpreted in the appropriate clinical context. In non-IgE-mediated food allergy, the diagnostic approach relies primarily on clinical history, a temporary elimination diet, and oral food challenge, which remains the gold standard for confirming the diagnosis in this form of allergy as well as in equivocal cases of IgE-mediated food allergy. The article highlights the most common interpretative errors, including the application of IgG/IgG4 testing, which lacks diagnostic value in food allergy and food intolerance. Accurate diagnosis of adverse food reactions should be conducted in accordance with current guidelines and integrated with the patient’s clinical presentation to enable appropriate diagnosis, risk assessment, and the avoidance of unnecessary elimination diets and their potential adverse health consequences.