Food allergy
A food allergy is an abnormal immune response to food. The symptoms of the allergic reaction may range from mild to severe. They may include itchiness, swelling of the tongue, vomiting, diarrhea, hives, trouble breathing, or low blood pressure. This typically occurs within minutes to several hours of exposure. When the symptoms are severe, it is known as anaphylaxis. A food intolerance and food poisoning are separate conditions, not due to an immune response.
Common foods involved include cow's milk, peanuts, eggs, shellfish, fish, tree nuts, soy, wheat, and sesame. The common allergies vary depending on the country. Risk factors include a family history of allergies, vitamin D deficiency, obesity, and high levels of cleanliness. Allergies occur when immunoglobulin E, part of the body's immune system, binds to food molecules. A protein in the food is usually the problem. This triggers the release of inflammatory chemicals such as histamine. Diagnosis is usually based on a medical history, elimination diet, skin prick test, blood tests for food-specific IgE antibodies, or oral food challenge.
Management involves avoiding the food in question and having a plan if exposure occurs. This plan may include giving adrenaline and wearing medical alert jewelry. Early childhood exposure to potential allergens may be protective against later development of a food allergy. The benefits of allergen immunotherapy for treating food allergies are not proven, thus not recommended as of 2015. Some types of food allergies among children resolve with age, including those to milk, eggs, and soy; while others such as to nuts and shellfish typically do not.
In the developed world, about 4% to 8% of people have at least one food allergy. They are more common in children than adults and appear to be increasing in frequency. Male children appear to be more commonly affected than females. Some allergies more commonly develop early in life, while others typically develop in later life. In developed countries, more people believe they have food allergies when they actually do not have them.
Signs and symptoms
Food allergy symptoms occur within minutes to hours after exposure and may include:- Rash
- Hives
- Itching of mouth, lips, tongue, throat, eyes, skin, or other areas
- Swelling of lips, tongue, eyelids, or the whole face
- Difficulty swallowing
- Runny or congested nose
- Hoarse voice
- Wheezing and/or shortness of breath
- Diarrhea, abdominal pain, and/or stomach cramps
- Lightheadedness
- Fainting
- Nausea
- Vomiting
Symptoms can vary. The amount of food needed to trigger a reaction also varies.
Serious danger regarding allergies can begin when the respiratory tract or blood circulation is affected. The former can be indicated through wheezing and cyanosis. Poor blood circulation leads to a weak pulse, pale skin and fainting.
A severe case of an allergic reaction, caused by symptoms affecting the respiratory tract and blood circulation, is called anaphylaxis. When symptoms are related to a drop in blood pressure, the person is said to be in anaphylactic shock. Anaphylaxis occurs when IgE antibodies are involved, and areas of the body that are not in direct contact with the food become affected and show symptoms. Those with asthma or an allergy to peanuts, tree nuts, or seafood are at greater risk for anaphylaxis.
Causes
Common food allergies
Allergic reactions are abnormal immune responses that develop after exposure to a given food allergen. Food allergens account for about 90% of all allergic reactions. The most common food allergens include milk, eggs, peanuts, tree nuts, fish, shellfish, soy, and wheat, which are referred to as "the big eight", and are required by US law to be on labels of foods that contain those foods. In April 2021, President Biden signed the FASTER Act into law. This recognized sesame as the ninth US mandatory food label allergen.Peanuts, a member of the legume family, are one of the most common food allergens that induce reactions in both children and adults. Affecting about 2% of the Western population, peanut allergies tend to cause more severe reactions and anaphylaxis than other food allergies. Tree nuts, including almonds, brazil nuts, cashews, coconuts, hazelnuts, macadamia nuts, pecans, pistachios, pine nuts, and walnuts, are also common allergens. Affected individuals may be sensitive to one particular tree nut or many different ones. Peanuts and seeds, including sesame seeds and poppy seeds, can be processed to extract oils, but trace amounts of protein may also elicit an allergic reaction. Peanut and tree nut allergies are lifelong conditions for the majority of those affected, although evidence shows that ~20% of those with peanut allergies and 9% of those with tree nut allergies may outgrow them.
Egg allergies affect about one in 50 children but are frequently outgrown when children reach age five. Affected individuals can be sensitive to proteins both in the egg white and egg yolk, but most children are allergic to those in the white while most adults are allergic to those in the yolk.
Cow's milk is the most common food allergen in infants and young children, yet many adults are also sensitized to cow's milk. Many affected individuals cannot tolerate dairy products such as cheese and yogurt. A small portion of children with milk allergy, roughly 10%, have a reaction to beef because it contains small amounts of protein that are also present in cow's milk.
Shellfish, which are divided into crustaceans and mollusks, are the most common food allergy in adults. People may be allergic to other types of seafood, such as fish. Fish allergies were found to be more common in countries that have high fish consumption compared to those with lower consumption.
Other common food allergens include soy and wheat. Those allergic to wheat may be sensitized to any protein in the wheat kernel. To a lesser frequency, people may be mildly allergic to raw fruits and vegetables, a disease known as oral allergy syndrome. Less common allergens include maize, spices, synthetic and natural colors, and chemical additives.
Balsam of Peru, which is in various foods, is in the "top five" allergens most commonly causing patch test reactions in people referred to dermatology clinics.
Routes of exposure
Exposure to certain food proteins triggers the production of antigen-specific immunoglobulin E antibodies, which, if unaccompanied by allergic symptoms, is known as allergic sensitization. Oral ingestion is the main sensitization route for most food allergy cases, yet other routes of exposure include inhalation and skin contact.For example, inhaling airborne particles in a farm-scale or factory-scale peanut shelling/crushing environment, or from cooking, can induce respiratory effects in allergic individuals. Furthermore, peanut allergies are much more common in adults who had oozing and crusted skin rashes as infants, suggesting that impaired skin may be a risk factor for sensitization. An estimated 28.5 million people worldwide are engaged in the seafood industry, which includes fishing, aquaculture, processing and industrial cooking. In these occupational settings, individuals with fish and shellfish allergies are at high risk of exposure to allergenic proteins via aerosolization. Respiratory symptoms may be induced by inhalation of wet aerosols from fresh fish handling, inhalation of dry aerosols from fishmeal processing, and dermal contact through skin breaks and cuts. Another occupational food allergy that involves respiratory symptoms is "baker's asthma," which commonly develops in food service workers who work with baked goods. Previous studies detected 40 allergens from wheat, some cross-reacted with rye proteins and a few cross-reacted with grass pollens.
Allergic sensitization can occur via skin antigen exposure, which usually manifests as hives. The skin has been suggested to be a critical sensitization route for peanut-allergic individuals. Peanut allergies are much more common in adults who had oozing and crusted skin rashes as infants, reinforcing that those with disrupted epithelial barriers, notably the skin barrier, are more prone to skin sensitization. Environmental factors, such as exposure to food, microorganisms, creams, and detergents, may lead to skin barrier dysfunction. Several studies reveal that children exposed to skin creams containing peanut oil are reported to have a higher risk of peanut allergy, suggesting that impaired skin may be a risk factor for sensitization.