Background

• A food allergy condition is an abnormal immune response to specific proteins found in certain foods. When a person with a food allergy condition consumes a specific food, their immune system mistakes the food protein as harmful and launches an attack against it. This can cause symptoms from mild to severe. 
• Some common symptoms of food allergies include itching, hives, swelling, nausea, vomiting, diarrhea, abdominal pain, difficulty breathing, and even anaphylaxis, a life-threatening allergic reaction. Anaphylaxis can cause a rapid drop in bp, difficulty breathing, and swelling of the throat, among other symptoms, and requires immediate medical attention. 
• Food allergies may develop at any age but are most commonly diagnosed in children. The most common food allergens include eggs, milk, peanuts, fish, shellfish, wheat, and soy. 
• Diagnosing a food allergy involves a combination of clinical history, physical examination, and allergy testing. The gold standard for allergy testing is a skin prick test, in which a very small amount of the suspected allergen is pierced into the skin, and the skin reaction is observed. Blood tests that measure the levels of specific allergy antibodies can also be used to confirm a diagnosis. 
• Currently, there is no known cure for food allergies. The primary treatment for food allergies is strict avoidance of the allergen. In case of accidental exposure, prompt treatment with antihistamines and epinephrine may be necessary to manage symptoms. It is vital for people with food allergies to carry an epinephrine auto-injector with them in case of an emergency. 

Epidemiology

• The prevalence of food allergies has been enhancing over the past few decades, particularly in developed countries. It is estimated that up to 10% of the population in Western countries have a food allergy. The prevalence of food allergies is more in children than in adults, with up to 8% of children under the age of 3 being affected. 
• The most common food allergens vary depending on age, geography, and ethnicity. In developed countries, milk, eggs, peanuts, fish, shellfish, wheat, and soy are the common food allergens. The most common food allergens in developing countries are typically cow’s milk, egg, and peanuts. 
• There are differences in the prevalence of food allergies among different ethnic groups. For example, peanut allergy is more common among children of African descent, while cow’s milk allergy is more common among children of European descent. 
• Food allergies can be life-threatening, and anaphylaxis from food allergies is responsible for many emergency department visits and hospitalizations yearly. In the United States, food allergy accounts for an estimated 200,000 emergency department visits and 30,000 hospitalizations annually. 
• Overall, food allergies have a significant impact on the healthy life of those affected, as well as on the healthcare system and the economy. Healthcare providers and public health officials need to continue to monitor and address the increasing prevalence of food allergies. 

Anatomy

Pathophysiology

• In individuals predisposed to specific allergens, food-specific IgE antibodies are created that attach to Fc epsilon receptors on basophils, mast cells, macrophages, and dendritic cells. When food allergens penetrate the mucosal barriers and interact with the IgE antibodies bound to these cells, these mediators are discharged, causing smooth muscle contractions, vasodilation, and the mucus secretion, leading to symptoms of hypersensitivity or allergy. Cytokines are released by activated mast cells and the macrophages that attract and also activate eosinophils, lymphocytes, resulting in prolonged inflammation that affects various body systems.  
• These symptoms include skin reactions such as angioedema, flushing, or urticaria; respiratory symptoms such as rhinorrhoea, nasal pruritus with the nasal congestion, dyspnoea, sneezing, laryngeal edema, and wheezing; gastrointestinal symptoms such as nausea, vomiting, oral pruritus, angioedema, diarrhea and abdominal pain, and cardiovascular symptoms such as loss of consciousness, hypotension, and dysrhythmias. 
• Approximately 40% of individuals with food allergies also experience chronic atopic dermatitis, and removing the specific food allergen from the diet can improve dermatitis.  
• Celiac disease results from an immune response system to dietary gluten, and in individuals with dermatitis herpetiformis, eliminating gluten from diet can also alleviate skin symptoms. 

Etiology

• The exact cause of food allergies is not understood, but it is generally believed to involve a combination of genetic and environmental factors. 
• Food allergies occur when the immune system mechanism mistakes a harmless food protein for a harmful substance and produces an allergic reaction to it. This immune response involves the production of immunoglobulin E (IgE) antibodies, which recognize the specific food protein and trigger the release of histamine and other chemicals in the body. 
• Genetic factor plays a key role in the development of food allergies. Children are likely to develop food allergies if they have a family history of allergies, asthma, or eczema. Specific genes are associated with an increased risk of developing food allergies. 
• Environmental factors can also contribute to the development of food allergies. Exposure to specific allergens early in life, such as peanuts or eggs, may increase the risk of an allergy to those foods. Other factors that might contribute to the development of food allergies include a weakened immune system, exposure to environmental pollutants, and changes in the gut microbiome. 
• There is also a theory known as the hygiene hypothesis, which suggests that the increase in food allergies and other allergic diseases may be partly due to a lack of exposure to certain microbes in early childhood. According to this theory, exposure to a diverse array of microbes helps to train the immune system to distinguish between harmful and harmless substances, including food proteins. 
• Overall, the development of food allergies is likely influenced by a complex interplay mechanism between genetic and environmental factors. Research in this area is ongoing, and a better understanding of the underlying causes of food allergies may lead to improved prevention and treatment strategies. 

Genetics

Prognostic Factors

The prognosis of food allergies varies depending on the severity of the allergy, the age at which it is diagnosed, and the specific allergen involved. 

Generally, food allergies are considered a lifelong condition, with most people requiring ongoing management to avoid exposure to the allergen and prevent allergic reactions. 

Prognostic factors that may influence the outcome of food allergies include: 

• Severity of the allergy: Individuals with severe food allergies, particularly those who have experienced anaphylaxis, are at greater risk of having a severe reaction in the future. 
• Age of diagnosis: Children diagnosed with food allergies at a younger age tend to be more likely to outgrow their allergies as they age. For example, many children with milk or egg allergies may outgrow them by the time they reach school age. 
• Type of allergen: The prognosis of food allergies may vary depending on the specific allergen involved. For example, peanut and tree nut allergies are less likely to be outgrown than milk or egg allergies. 
• Coexisting conditions: Individuals with asthma or other allergies may be at higher risk for severe reactions to food allergens. 
• Compliance with avoidance measures: Individuals who can strictly avoid exposure to their allergen have a better prognosis than those who have difficulty adhering to avoidance measures. 

Clinical History

The clinical presentation of food allergies may also vary depending on the comorbidities and activities of the individual, as well as the acuity of the reaction. 

• Age group: Food allergies can affect individuals of any age group, including infants, children, adolescents, and adults. 

Physical Examination

Physical examination alone is not sufficient to diagnose food allergies. However, there may be some physical signs that are associated with food allergies, such as: 

• Skin changes: Food allergies can cause various skin changes, including hives (raised, red, itchy bumps on the skin), eczema (dry, scaly, and itchy patches of skin), and swelling (particularly of the lips, tongue, and face). 
• Respiratory symptoms: Food allergies can also cause respiratory symptoms, such as wheezing, coughing, shortness of breath, and nasal congestion. 
• Gastrointestinal symptoms: Some individuals with food allergies may experience gastrointestinal symptoms, such as vomiting, nausea, abdominal pain, and diarrhea. 

In addition to a physical examination, a thorough medical history and diagnostic testing are necessary to diagnose food allergies. This may include allergy skin testing, blood tests for specific IgE antibodies, and food challenges (in which the individual is given small amounts of the suspected allergen under medical supervision to monitor for a reaction). 

Age group

Associated comorbidity

• Individuals with other allergic conditions, such as asthma, atopic dermatitis, or allergic rhinitis, may be at higher risk for food allergies.
• Exercise or physical activity may also trigger or worsen symptoms in some individuals with food allergies. 

Associated activity

Acuity of presentation

• The onset and severity of symptoms may vary depending on the individual person and the allergen involved. In some cases, symptoms may occur within minutes of exposure to the allergen, while in other cases, symptoms may be delayed and may not appear until several hours after exposure. 

Symptoms of food allergies may include: 

• Skin reactions: Hives, eczema, itching, and swelling of the lips, tongue, and face. 
• Respiratory symptoms: Wheezing, coughing, shortness of breath, and nasal congestion. 
• Gastrointestinal symptoms: Vomiting, nausea, abdominal pain, and diarrhea. 
• Cardiovascular symptoms: Palpitations, dizziness, and fainting. 
• Anaphylaxis: A severe and potentially life-threatening allergic symptoms, including difficulty breathing, swelling of tongue and throat, a rapid drop in blood pressure, and loss of consciousness. 

Differential Diagnoses

The differential diagnosis of food allergies can include various conditions that may present with similar symptoms. Some of these conditions include: 

• Food intolerances: These can cause symptoms similar to food allergies but do not involve the immune system. Examples include lactose intolerance or fructose malabsorption. 
• Gastrointestinal disorders: Conditions such as esophagitis, gastroesophageal reflux disease (GERD), irritable bowel syndrome (IBS), or inflammatory bowel disease (IBD) can cause gastrointestinal symptoms such as nausea, abdominal pain, and diarrhea. 
• Gastroenteritis: It is a digestive system infection caused by viruses, bacteria, or parasites. It can cause symptoms such as vomiting, diarrhea, and abdominal pain, which may be similar to those of food allergies. 
• Factitious disorder: In some cases, individuals may fake or exaggerate symptoms of food allergies or intentionally induce an allergic reaction for psychological reasons. 
• Esophageal motility disorders: These conditions affect food movement through the esophagus, causing symptoms such as difficulty swallowing or chest pain. 
• Lactose intolerance: It is a condition in which the body cannot digest lactose, a sugar found in milk and dairy products. It can cause symptoms such as bloating, abdominal pain, and diarrhea. 
• Giardiasis: This parasitic infection can cause diarrhea, abdominal pain, and other gastrointestinal symptoms. 
• Whipple disease: This rare bacterial infection can cause gastrointestinal symptoms such as abdominal pain, diarrhea, and weight loss. 

Laboratory Studies

Imaging Studies

Procedures

Histologic Findings

Staging

Treatment Paradigm

• The management of food allergies involves several approaches, including modification of the environment, administration of pharmaceutical agents, and intervention with procedures.
• The management phase may also vary depending on the severity of the allergy and the individual’s response to treatment. 

by Stage

by Modality

Chemotherapy

Radiation Therapy

Surgical Interventions

Hormone Therapy

Immunotherapy

Hyperthermia

Photodynamic Therapy

Stem Cell Transplant

Targeted Therapy

Palliative Care

• The most effective way to manage food allergies is to avoid exposure to the allergen.
• This may involve reading food labels, avoiding cross-contamination during food preparation, and informing family, friends, and healthcare providers about the allergy. 

• Medications may be used to treat symptoms of food allergies, such as antihistamines to relieve itching and swelling, corticosteroids to reduce inflammation, and epinephrine (adrenaline) to treat anaphylaxis. Individuals with severe allergies may be prescribed an epinephrine auto-injector and educated on how to use it in case of an emergency. 

• In some cases, medical procedures may be necessary to manage food allergies. For example, oral immunotherapy (OIT) involves gradually exposing an individual to increasing doses of the allergen to help desensitize the immune system. This may be done under medical supervision in a clinic or hospital setting. Other procedures, such as allergy shots (immunotherapy) or patch testing, may also be recommended in some cases. 

• The management phase may vary depending on the individual’s response to treatment. In the acute phase, immediate treatment may be necessary to manage symptoms and prevent anaphylaxis. In the subacute phase, ongoing management may involve avoidance measures, medications, and emergency action plans. In the long-term phase, some individuals may be able to undergo immunotherapy to desensitize the immune system and reduce the risk of severe reactions. 

Medication

Future Trends

Media Gallary

References

• https://www.ncbi.nlm.nih.gov/books/NBK482187/#article-21877.s5