Difference between allergy, sensitivity and intolerance
Depends on the source of information, there are several different versions of adverse food reactions categorisation. Sometimes adverse food reactions have been categorised only to food allergy and food intolerance and in some occasions food intolerance has been regarded interchangeable to food sensitivity.
At this point, in order to better clarify the difference between each category scientifically and also to avoid further confusion among general perception about each category, the adverse reactions to food or ingestible ingredients has been categorised in to three main groups as food allergy, food sensitivity and food intolerance. As the concept of food allergy among the general population and even the healthcare professionals often has been regarded as type I food allergy or IgE mediated food allergy, here we try to maintain the same concept and use the term "Sensitivity" for describing other immune mediated food allergies. Food sensitivity and food intolerance are also divided into more detailed categories according to their mechanisms of reaction.
The term "Food Hypersensitivity" refers to all types of unusual clinical overreactions following ingestion of food, beverages and food additives. It is used broadly to describe any food allergy (immediate or delayed), food intolerance (enzymatic/metabolic, pharmacologic, toxic and undefined) and unspecified food reactions. Symptoms of food hypersensitivity are many and range from mild to life threatening. They also could manifest in only one part or different parts of the body individually or simultaneously.
Immediate food allergy
Food allergy, (also know as true food allergy, type I allergy or IgE mediated food allergy) is when the immune system reacts unusually to certain foods. Symptoms of food allergy can vary from mild to severe and sometimes life threatening. The symptoms normally appear within 2-15 minutes of ingesting the food and may affect one part or different areas of the body at the same time. Often a tiny amount of the allergy-causing food can trigger signs and symptoms of food allergy such as:
- Skin rash, itching, hives/urticaria
- Swelling of the lips, tongue, throat, face
- Shortness of breath, trouble breathing, wheezing, chest tightness
- Stomach pain, vomiting, diarrhea
- Feeling of impending doom, confusion, faint
The most common foods causing allergy are milk, egg, nuts, peanuts, fish and shellfish. Food allergy is often diagnosed by skin prick test or food-specific IgE antibody test in conjunction with clinical history. Occasionally, food challenge test is used to confirm the result of skin prick test or blood test. Some people may outgrow their food allergies (especially younger children), while those with severe reactions likely to retain it for life.
Delayed food allergy
Delayed food allergy triggers immune system reaction, however the reaction either does not involve IgE antibodies, or it is a mixed of IgE and non-IgE antibodies. Symptoms of delayed food allergy often emerge between 2-48 hours of ingesting ( or touching in case of contact dermatitis) the offending food. The symptoms are often dose dependant, which means ingesting a tiny amount of the offending food unlikely to trigger any noticeable symptoms. Consumption of certain amount of the offending food is usually needed to trigger the symptoms. It sometimes require frequent consumption of the offending food over a few days, weeks or even several months to provoke the symptoms. The symptoms could involve the gut, lungs, skin, musculoskeletal and nervous system, however they are not life threatening except FPIES reaction. Most people affected by delayed food allergy outgrow their condition with the exception of Celiac disease which is a lifelong disorder. Delayed food allergy is categorised into three major groups depends on the mechanism and immunoglobulin antibodies involved. Each group and related health conditions/disorders are explained below:
Non IgE Mediated reaction
Non-IgE mediated food allergies are caused by a reaction involving other components of the immune system including T cells, B cells, macrophages and mast cells. Symptoms of such reactions are typically delayed and often take several hours or days to develop and may involve gastrointestinal, cutaneous or respiratory symptoms; nonetheless gastrointestinal reactions are the most common reactions. The most common reactions in this category are: Food protein induced enterocolitis syndrome (FPIES), Food protein induced proctocolitis, Food protein induced enteropathy, Cow’s milk-induced gastro-oesophageal reflux, Cow’s milk-induced constipation, Celiac disease, Heiner Syndrome
Mixed IgE & Non IgE Mediated reaction
Mixed IgE and non-IgE mediated reactions are conditions associated with food allergy involving IgE and T-Cell mediated mechanisms. Disorders that fall into this category include atopic dermatitis and the eosinophilic gastroenteropathies (Eosinophilic esophagitis, Eosinophilic gastritis, Eosinophilic enteritis, Eosinophilic colitis). Some people with atopic dermatitis or eosinophilic gastroenteropathies may have positive IgE reaction to certain food, while for others the reaction is delayed involving T-Cell mediated mechanism.
Cell Mediated Reaction
Adverse food reactions do not always occur through ingestion, but they may also be due to inhalation or through contact with the food and spices. Following contact with the offending food, dermatitis can develop either as a result of direct exposure when a certain type of food is touched (allergic hand contact dermatitis) or another less obvious route of exposure through the aerosolization of aromatic particles (eyelid contact dermatitis). This allergic condition does not involve the IgE antibody, but it is generally through T cell- mediated mechanism. Allergic contact dermatitis to foods, spices, and food additives typically occurs to individuals handling food or working in food industry. The common reaction location is on hands following contact with garlic, onion, lemon and spices.
Non-Specific Food Sensitivity
Unclassified food reaction is relatively a new concept in adverse food reactions that hardly has been discussed in any scientific paper or session. It appears that in some people presence or severity of certain health conditions are somehow connected to the ingestion of certain foods. The best examples to describe the nonspecific food reaction is among patients with irritable bowel syndrome . It is evident that not all patients with IBS may related presence or severity of their abdominal symptoms to the type of the food they consume, yet many believe that certain food trigger or worsen their IBS symptoms significantly. The mechanism of IBS remain uncertain, however emerging evidence is indicating a role for immune system in the pathophysiology of the disorder. Similarly, it is not yet clear through which mechanism certain foods trigger or exacerbate IBS syndrome in some patients. In addition, a series of newly conducted research show that elimination of certain foods lead to significant reduction of certain symptoms of inflammatory bowel disease and incorporation of the same foods triggers the symptoms. It is not yet known if the mechanism involved in the exacerbation of the symptoms is immune mediated, non-immune mediated or a combination of both.
Another example of non-specific adverse food reaction could be seen in people who experience gastrointestinal symptoms such as vomiting, abdominal cramping and diarrhea 30 minutes to several hours after ingesting seafood, particularly shrimp, shellfish and prawn. In fact, about a quarter of people who react to seafood may only experience gastrointestinal symptoms without other classic allergy symptoms such as hives (urticaria), angioedema (swelling), rash, itchy skin, runny nose, coughing, difficulty breathing, asthma and anaphylactic shock . Among these individuals majority have delayed digestive symptoms in the absence of IgE sensitization, which means blood specific IgE test and skin prick test doesn't provide positive result. The symptoms in these people are similar to infants and young children with food protein induced enterocolitis syndrome (FPIES), however the main differences between these two conditions rely on the age and resolution of the adverse reaction by age. FPIES is predominantly seen in infants and young children and the reaction usually disappears as the child grows and reaches age 2-3, nonetheless unspecified digestive reaction to seafood in the absence of IgE sensitization typically beings at adulthood and there is no evidence to suggest that the condition resolves with time and age.
Food intolerance is an abnormal physiological response (non immune mediated) to a food, beverage, food additives, or compound found in foods that produces symptoms in one or more body organs and systems. The reaction is often delayed and may involve the skin, digestive system, nervous system, respiratory system and circulatory system. Food intolerance may cause skin rashes, hives/urticaria, eczema, gas, bloating, diarrhea, constipation, stress, anxiety, panic attack, palpitation, asthma, nasal congestion, sinusitis, headaches, migraines and many more symptoms.
Metabolic food reactions are due to genetically-inherited defect or acquired errors of metabolism of a food component, usually due to enzyme dysfunction or enzyme deficiency. Examples of such adverse reactions include lactose intolerance, fructose malabsorption, diabetes, phenylketonuria, favism, maple syrup urine disease, glucose galactose malabsorption and galactosemia. Symptoms of metabolic food reactions are vary and may present as digestive symptoms, neurological and psychological disorders and anaemia. Depends on the type of the metabolic food reaction there are different tests to ascertain the disorder.
Pharmacological reactions are generally due to certain naturally occurring compounds in foods, such as salicylates and amines and also to caffeine and alcohol. These chemicals are capable of producing a drug-like (pharmacologic) side effects in susceptible individuals. Symptoms of such reactions vary and depends on the offending compound may include rashes, asthma effect, coughing, palpitation, panic attack, flushing, psychological and neurological symptoms.
Toxins may either be present naturally in food, be released by bacteria, or be due to contamination of food products. Toxic food reactions are caused by the direct action of a food or substance without immune involvement. For example some legumes and beans contain naturally occurring toxins such as lectins (ricin), which if consumed uncooked or undercooked may cause gastrointestinal symptoms. Certain fish, such as tuna or mackerel, that are not refrigerated properly and that contain high amounts of bacteria may produce high levels of histamine which causes histamine toxicity, also known as scombroid poisoning, and triggers digestive symptom, flushing and headaches.
Idiopathic or Undefined
Idiopathic food reaction or undefined food reactions include any adverse food reaction due to an unknown mechanism. Reaction to food additives are generally considered in this category. Some susceptible individuals may show unusual reactions to sulphites, nitrates, benzoate, monosodium glutamate and some food colourings. The symptoms typically include runny noses, sneezing, migraines, rashes, asthma, coughing and digestive symptoms.