Many food allergens not actually included in the European priority list of allergenic foods have the potential to cause severe allergic reactions and could escape correct identification and behave as "hidden allergens". Moreover, the adoption in recent years of novel diets based on plant products and new sustainable foods or the use of specific food additives have contributed to the onset of new emerging allergens of public health importance. The knowledge of hidden allergens is important both for physicians and for patients to improve the prevention, diagnosis and treatment of food allergies, in order to decrease eventual improper diagnosis of idiopathic anaphylaxis. In this review, the characteristics of the most frequent hidden allergens and their diagnostic tools are described. A detailed history with a careful review of the ingredient lists, an understanding of possible cross-reactions or contaminations with other foods, together with an allergological evaluation consisting of