Updated | 31 March 2020 What is food allergy? Food allergy is an overreaction of the immune system against food proteins. This food allergy reaction can happen following exposure to food by different routes: Food; Contact with skin or mucous membranes; Vapors from cooking food. How does food allergy happen? Food allergy can involve different immunological mechanisms, which determines quite different presentations. Immunoglobulin (Ig) E or IgE-mediated food allergy This is the most common form, which results from the production of IgE antibodies against food. The reaction is immediate , the symptoms appear in the first 30 minutes or up to 2 hours after contact with the food, and can be very severe, even fatal, even with a little amount of the food. Non-IgE-mediated food allergy Other immunological mechanisms, cells or antibodies are involved. This is usually a delayed reaction , starting more than 2 hours after eating the food, which can make food allergy suspicion difficult. What are the symptoms of food allergy? Symptoms of food allergy can include several organs or body systems. Skin and mucous membranes Regardless of the allergens, the most frequent symptoms involve the skin and / or mucous membranes, and include hives, angioedema, itchy oropharyngeal / oral allergy syndrome, edema of the glottis. Urticaria and angioedema: appearance of red and itchy skin lesions frequently associated with angioedeme when deeper layers of the skin or mucous membranes are reached. Angioedema often involves the eyelids, lips, mucous membranes and extremities, with a slower resolution compared to urticaria. Oral allergy syndrome: Edema (swelling), itching and / or tingling of the lips, tongue, oropharynx or the entire oral cavity. Arises when the food, usually a plant food, contacts the oral mucosa. Digestive system Allergic reactions can also involve the digestive system, with vomiting, diarrhea, abdominal pain. Respiratory and cardiovascular system Allergy symptoms can also involve the respiratory system - rhinitis, cough, wheezing and difficulty breathing - and / or the cardiovascular system - tachycardia, hypotension, lipothymia. • Anaphylaxis Anaphylaxis is the most serious form of an allergic reaction. It is characterized by the occurrence of symptoms involving two or more body organs or systems . Usually, this systemic reaction develops quickly after exposure to the allergen and is life-threatening when it is not treated promptly and adequately. Late allergic reactions (ie, non-IgE-mediated and / or mixed) can lead to vomiting, eczema, blood in the stools, diarrhea with mucus, episodes of food impact or growth retardation. What foods are related with food allergy? Any food can trigger food allergy . However, the causal food varies with patients age and eating habits of each family, which are closely related to the country where they live. Like in most developed countries, in Portugal food allergies are increasingly frequent and serious , mainly in pediatric age. National screenings reveal that food allergy affects 5% -10% of children, with a predominance of cow's milk and egg allergies. Allergies to the following foods are also common: Wheat, Fish, Shellfish (crustaceans and molluscs), Dried fruits, seeds, peanuts, Legumes, Fresh fruits, Some vegetables. The severity of food allergic reactions is often associated with the food involved. The same food can contain a wide variety of allergens and the severity of the reactions can vary depending on the type of allergens to which patients are sensitive. What is food intolerance? Food intolerance is also an overreaction of the body to a particular food , but it does not result from immunological mechanisms . Food intolerance is related, for example, to the digestion or transformation of food in the body. One of the most common food intolerances is lactose intolerance , which occurs in individuals with partial or total lactase deficiency (the enzyme that digests lactose). The chemical composition of the food, eg content of salicylates or amines, can also induce reactions in more sensitive individuals. Generally, food intolerance reactions are dose-dependent and do not have a poor prognosis although they can have a significant negative impact on quality of life. Common food intolerance symptoms are: Dgestive complaints, such as bloating, flatulence, irritable bowel, recurrent abdominal pain; Headache; Joint pain; Fatigue and general disconfort. How is the diagnosis of a food allergy or food intolerance made? If you suspect you are allergic or intolerant to a certain food, you should consult an allergologist . The diagnosis of food allergy is based primarily on a detailed clinical history . Diagnostic tests will be indicated according to the type of allergy that is suspected and can be: Skin allergy tests; Blood tests; Digestive endoscopy for allergic diseases of the digestive system; Oral food provocation test to identify food involved. The diagnostic approach to food intolerance is "trial and error" phased process. How are food allergy and food intolerance treated? After confirmation of food allergy or intolerance, it becomes necessary, in any case, to exclude the food from the diet. This task is not always easy. It forces you to carefully read the labels of food products in order to identify potential allergens. It is also important to avoid nutritional deficits that may occur due to the exclusion of the food in question. It is essential to plan the treatment of any accidental allergic reactions due to accidental exposure to food. In severe cases of anaphylaxis, the patient and, in the case of the child, his family, must have available devices for self-administration of adrenaline . The school / nursery should have detailed information about the child medical condition and emergency treatment should be available. More recently, innovative therapeutic strategies have emerged, such as the induction of tolerance or oral food desensitization , a procedure to be carefully used, always under the supervision of experienced immunoallergologists, in specialized centers. Authors of this text are the following allergologists from Hospital da Luz network: Luís Miguel Borrego, Ana Morais Mendes, Ana Reis Ferreira, Andreia Ferrão, Carlos Braga, Cristina Lopes, Diana Pereira da Silva, Filipa Semedo, Isabel Costa Silva, João Gaspar Marques, Pedro Carreiro Martins, Marta Salgado, Nuno Sousa, Rosa Anita Fernandes, Susana Piedade The content published in the Health Guide is intended for the general public and is provided for informational and educational purposes only. It does not replace individual medical assessment, diagnosis, or personalized clinical advice from a qualified healthcare professional. The content is produced or reviewed by physicians and other healthcare professionals at Hospital da Luz and is based on the knowledge available at the time of publication or the most recent update, as indicated at the beginning of each item.
