Food allergies can have fast onset (from seconds to one hour) or slow onset (from hours to several days) depending on mechanism. Symptoms 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, shortness of breath, diarrhea, abdominal pain, lightheadedness, fainting, nausea and vomiting. Symptoms of allergies vary from person to person and may vary from incident to incident. Serious danger regarding allergies can begin when the respiratory tract or blood circulation is affected. The former can be indicated by wheezing, a blocked airway and cyanosis, the latter by weak pulse, pale skin, and fainting. When these symptoms occur the allergic reaction is called anaphylaxis. 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 severe symptoms. Untreated, this can proceed to vasodilation, a low blood pressure situation called anaphylactic shock, and death (very rare).

For milk allergy, non-IgE-mediated responses are more common than IgE-mediated. Non-IgE mediated reactions can manifest as dermatitis/eczema and gastrointestinal symptoms, especially in infants and young children. Infants exhibit dermatiis on face, scalp and other parts of the body, while in slightly older children knees and elbows are more commonly afflicted. Children with dermatitis are at greater than expected risk of also exhibiting asthma and allergic rhinitis.

Food allergies can have fast onset (from seconds to one hour) or slow onset (from hours to several days) depending on mechanism. Symptoms 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, shortness of breath, diarrhea, abdominal pain, lightheadedness, fainting, nausea and vomiting. Symptoms of allergies vary from person to person and may vary from incident to incident. Serious danger regarding allergies can begin when the respiratory tract or blood circulation is affected. The former can be indicated by wheezing, a blocked airway and cyanosis, the latter by weak pulse, pale skin, and fainting. When these symptoms occur the allergic reaction is called anaphylaxis. 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 severe symptoms. Untreated, this can proceed to vasodilation, a low blood pressure situation called anaphylactic shock, and death (very rare).

Food allergies usually have a fast onset (from seconds to one hour) and may include:

- Rash

- Hives

- Itching of mouth, lips, tongue, throat, eyes, skin, or other areas

- Swelling (angioedema) 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

In some cases, however, onset of symptoms may be delayed for hours.

Symptoms of allergies vary from person to person. The amount of food needed to trigger a reaction also varies from person to person.

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.

Food allergies usually have a fast onset (from seconds to one hour). Symptoms 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, shortness of breath, diarrhea, abdominal pain, lightheadedness, fainting, nausea, or vomiting. Symptoms of allergies vary from person to person and may vary from incident to incident. Serious danger regarding allergies can begin when the respiratory tract or blood circulation is affected. The former can be indicated by wheezing, a blocked airway and cyanosis, the latter by weak pulse, pale skin, and fainting. When these symptoms occur the allergic reaction is called anaphylaxis. 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 severe symptoms. Untreated, this can proceed to vasodilation, a low blood pressure situation called anaphylactic shock, and death (very rare).

Young children may exhibit dermatitis/eczema on face, scalp and other parts of the body, in older children knees and elbows are more commonly afflicted. Children with dermatitis are at greater than expected risk of also exhibiting asthma and allergic rhinitis.

Wheat allergy is an allergy which typically presents itself as a food allergy, but can also be a contact allergy resulting from occupational exposure to wheat. Like all allergies, wheat allergy involves immunoglobulin E and mast cell response. Typically the allergy is limited to the seed storage proteins of wheat, some reactions are restricted to wheat proteins, while others can react across many varieties of seeds and other plant tissues. Wheat allergy may be a misnomer since there are many allergenic components in wheat, for example serine protease inhibitors, glutelins and prolamins and different responses are often attributed to different proteins. Twenty-seven potential wheat allergens have been successfully identified. The most severe response is exercise/aspirin induced anaphylaxis attributed to one omega gliadin that is a relative of the protein that causes celiac disease. Other more common symptoms include nausea, urticaria, atopy. Gluten sensitivity is not usually classified as a wheat allergy.

A food allergy is an abnormal immune response to food. The signs and symptoms 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. Food intolerance and food poisoning are separate conditions.

Common foods involved include cow's milk, peanuts, eggs, shellfish, fish, tree nuts, soy, wheat, rice, and fruit. 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 (IgE), 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.

Early exposure to potential allergens may be protective. Management primarily involves avoiding the food in question and having a plan if exposure occurs. This plan may include giving adrenaline (epinephrine) and wearing medical alert jewelry. The benefits of allergen immunotherapy for food allergies is unclear, thus is not recommended as of 2015. Some types of food allergies among children resolve with age, including that 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, a large proportion of people believe they have food allergies when they actually do not have them.

Milk allergy is an adverse immune reaction to one or more of the protein constituents of cow's milk. Symptoms can be rapid or gradual in onset. The former may include anaphylaxis, a potentially life-threatening condition which requires treatment with epinephrine. The latter can take hours to days to appear. Presentations may include atopic dermatitis, inflammation of the esophagus, enteropathy involving the small intestine and proctocolitis involving the rectum and colon.

In the United States, 90% of allergic responses to foods are caused by eight foods: cow's milk, eggs, wheat, shellfish, peanuts, tree nuts, fish, and soy beans. Allergy to cow's milk is the most common. The U.S. Food Allergen Labeling and Consumer Protection Act of 2004 requires that the label of a food that contains an ingredient that is or contains protein from these eight major food allergens declare the presence of the allergen on the label. Dairy foods are also on the mandatory labeling list in Japan and the European Union.

Prevention is by avoiding eating foods that contain dairy. Infants should be breastfed for at least four months, preferably six months before introduction of cow's milk. If there is a family history of dairy allergy then an extensively hydrolyzed cow's milk formula is recommended. Soy infant formula can be considered, but about 10 to 15% of babies allergic to cow's milk will also react to soy. In the United States, milk allergy affects between 2% and 3% of babies and young children. The majority of people outgrow milk allergy. Predictors for adult-persistence are anaphylaxis, high milk-specific serum immunoglobulin E (IgE), robust response to the skin prick test and absence of tolerance to milk-containing baked foods. Oral immunotherapy is being researched, but as of 2014 it is of unclear benefit.

OAS sufferers may have any of a number of allergic reactions that usually occur very rapidly, within minutes of eating a trigger food. The most common reaction is an itching or burning sensation in the lips, mouth, ear canal, or pharynx. Sometimes other reactions can be triggered in the eyes, nose, and skin. Swelling of the lips, tongue, and uvula and a sensation of tightness in the throat may be observed. It can seldom result in anaphylaxis. If a sufferer swallows the food, and the allergen is not destroyed by the stomach acids, there is a good chance that there will be a reaction from histamine release later in the gastrointestinal tract. Vomiting, diarrhea, severe indigestion, or cramps may occur. Rarely, OAS may be severe and present as wheezing, vomiting, hives and low blood pressure.

The symptoms may vary depending upon the person, the severity of the allergy, and type of fruit. For example, mango allergy symptoms include hoarseness, dyspnoea and bronchitic rales (asthma) (Sareen and Shah). The duration of the symptoms tested by Saree and Shah were variable and ranged from 4 h [11] to 7 days [12]. The symptoms may appear within a few minutes.

Allergic reactions to fruit and vegetables are usually mild and often just affect the mouth, causing itching, a rash, or blisters where the food touches the lips and mouth. This is called oral allergy syndrome. A number of people who react in this way to fruit or vegetables will also react to pollen from some trees and weeds. So, for example, people who are allergic to birch pollen are also likely to be allergic to apples.

Another symptom may include slight swelling in the throat, making it feel like it is closing. The ability to breathe is still present though, so it is not fatal.

Some rice proteins are regarded as the causes of allergy in people. People allergic to rice might have sneezing, runny nose, itching, asthma, stomachache or eczema after they eat rice. Besides eating rice, people with a rice allergy can have reactions breathing rice steam from cooked rice. Allergic people might have skin rashes and swellings. Moreover, they might stop breathing and die due to their stopped heart.

Egg allergy is an immune hypersensitivity to proteins found in chicken eggs, and possibly goose, duck, or turkey eggs. Symptoms can be either rapid or gradual in onset. The latter can take hours to days to appear. The former may include anaphylaxis, a potentially life-threatening condition which requires treatment with epinephrine. Other presentations may include atopic dermatitis or inflammation of the esophagus.

In the United States, 90% of allergic responses to foods are caused by cow's milk, eggs, wheat, shellfish, peanuts, tree nuts, fish, and soy beans. The Food Allergen Labeling and Consumer Protection Act (FALCPA) of 2004 requires that the label of a food that contains an ingredient that is or contains protein from these eight major food allergens declare the presence of the allergen in the manner described by the law. Eggs are also on the mandatory labeling list in Japan and the European Union.

Prevention is by avoiding eating eggs and foods that may contain eggs, such as cake or cookies. It is unclear if the early introduction of the eggs to the diet of babies aged 4–6 months decreases the risk of egg allergies.

Egg allergy appears mainly in children but can persist into adulthood. In the United States, it is the second most common food allergy in children after cow's milk. Most children outgrow egg allergy by the age of five, but some people remain allergic for a lifetime. In North America and Western Europe egg allergy occurs in 0.5% to 2.5% of children under the age of five years. The majority grow out of it by school age, but for roughly one-third, the allergy persists into adulthood. Strong predictors for adult-persistence are anaphylaxis, high egg-specific serum immunoglobulin E (IgE), robust response to the skin prick test and absence of tolerance to egg-containing baked foods.

Soy allergy is a type of food allergy. It is a hypersensitivity to dietary substances from soy causing an overreaction of the immune system which may lead to severe physical symptoms for millions of people. The Asthma and Allergy Foundation of America estimates soy is among the eight most common food allergens for pediatric and adult food allergy patients. It is usually treated with an exclusion diet and vigilant avoidance of foods that may be contaminated with soy ingredients. The most severe food allergy reaction is called anaphylaxis and is a medical emergency requiring immediate attention and treatment with epinephrine.

Wheat allergies are not altogether different from other food allergies or respiratory allergies. However two conditions, exercise/aspirin induced anaphylaxis and urticaria occur more frequently with wheat allergies.

Common symptoms of a wheat allergy include sacroiliitis, eczema (atopic dermatitis), hives (urticaria), asthma, "Hay fever" (allergic rhinitis), angioedema (tissue swelling due to fluid leakage from blood vessels), abdominal cramps, nausea, and vomiting. Rarer symptoms include anaphylactic shock, anxiety, arthritis, bloated stomach, chest pains, depression or mood swings, diarrhea, dizziness, headache, joint and muscle aches and pains (may be associated with progressive arthritis), palpitations, psoriasis, irritable bowel syndrome (IBS), swollen throat or tongue, tiredness and lethargy, and unexplained cough.

Reactions may become more severe with repeated exposure.

Peanut allergy is a type of food allergy to peanuts. It is different from nut allergies. Physical symptoms of allergic reaction can include itchiness, urticaria, swelling, eczema, sneezing, asthma, abdominal pain, drop in blood pressure, diarrhea, and cardiac arrest. Anaphylaxis may occur.

It is due to a type I hypersensitivity reaction of the immune system in susceptible individuals. The allergy is recognized "as one of the most severe food allergies due to its prevalence, persistency, and potential severity of allergic reaction."

Prevention may be partly achieved through early introduction of peanuts to the diets of pregnant women and babies. The principal treatment for anaphylaxis is epinephrine as an injection.

In the United States, peanut allergy is present in 0.6% of the population. It is a common cause of food-related fatal and near-fatal allergic reactions.

Oral allergy syndrome (OAS) is an allergic reaction in the mouth following eating food. It is a type of food allergy classified by a cluster of allergic reactions in the mouth in response to eating certain (usually fresh) fruits, nuts, and vegetables that typically develops in adults with hay fever.

OAS is perhaps the most common food-related allergy in adults. OAS is not a separate food allergy, but rather represents cross-reactivity between distant remnants of tree or weed pollen still found in certain fruits and vegetables. Therefore, OAS is only seen in people with seasonal pollen allergies, and mostly people who are allergic to tree pollen. It is usually limited to ingestion of only uncooked fruits or vegetables.

Another term used for this syndrome is pollen-food allergy. In adults up to 60% of all food allergic reactions are due to cross-reactions between foods and inhalative allergens.

OAS is a Type 1 or IgE-mediated immune response, which is sometimes called a "true allergy". The body's immune system produces IgE antibodies against pollen; in OAS, these antibodies also bind to (or cross-react with) other structurally similar proteins found in botanically related plants.

OAS can occur any time of the year but is most prevalent during the pollen season. Individuals with OAS usually develop symptoms within a few minutes after eating the food.

Rice allergy is a type of food allergy. People allergic to rice react to some rice proteins after they eat rice or breathe in rice steam. Although some reactions might lead to severe health problems, doctors can diagnose rice allergy with many methods and help allergic people to avoid reactions.

Many allergens such as dust or pollen are airborne particles. In these cases, symptoms arise in areas in contact with air, such as eyes, nose, and lungs. For instance, allergic rhinitis, also known as hay fever, causes irritation of the nose, sneezing, itching, and redness of the eyes. Inhaled allergens can also lead to increased production of mucus in the lungs, shortness of breath, coughing, and wheezing.

Aside from these ambient allergens, allergic reactions can result from foods, insect stings, and reactions to medications like aspirin and antibiotics such as penicillin. Symptoms of food allergy include abdominal pain, bloating, vomiting, diarrhea, itchy skin, and swelling of the skin during hives. Food allergies rarely cause respiratory (asthmatic) reactions, or rhinitis. Insect stings, food, antibiotics, and certain medicines may produce a systemic allergic response that is also called anaphylaxis; multiple organ systems can be affected, including the digestive system, the respiratory system, and the circulatory system. Depending on the rate of severity, it can cause a skin reactions, bronchoconstriction, swelling, low blood pressure, coma, and death. This type of reaction can be triggered suddenly, or the onset can be delayed. The nature of anaphylaxis is such that the reaction can seem to be subsiding, but may recur throughout a period of time.

Reported symptoms of NCGS are similar to those of celiac disease, with most patients reporting both gastrointestinal and non-gastrointestinal symptoms. In the "classical" presentation of NCGS, gastrointestinal symptoms are similar to those of irritable bowel syndrome, and are also not distinguishable from those of wheat allergy, but there is a different interval between exposure to wheat and onset of symptoms. Wheat allergy has a fast onset (from minutes to hours) after the consumption of food containing wheat and can be anaphylaxic.

As a result of a possible immunoglobulin E (IgE) allergy to corn, symptoms can resemble that of any other recognized allergy, including anaphylaxis. Reactions to corn derivatives, such as corn syrup, are also possible.

Gastrointestinal symptoms may include any of the following: abdominal pain, bloating, bowel habit abnormalities (either diarrhea or constipation), nausea, aerophagia, gastroesophageal reflux disease, and aphthous stomatitis.

A typical allergic reaction to alpha-gal has a delayed onset, occurring 3–8 hours after the consumption of mammalian meat products, instead of the typical rapid onset with most food allergies. After the delayed onset, the allergic response is typical of most food allergies, and especially an IgE mediated allergy, including severe whole-body itching, hives, angioedema, gastrointestinal upset, and possible anaphylaxis. In 70% of cases the reaction is accompanied by respiratory distress and as such is particularly harmful to those with asthma.

Alpha-gal allergies are the first food allergies to come with the possibility of delayed anaphylaxis. It is also the first food-related allergy to be associated with a carbohydrate, rather than a protein.

Dermatitis herpetiformis (DH), or Duhring-Brocq disease, is a chronic blistering skin autoimmune condition, characterized by the presence of skin lesions that have an extensive and symmetrical distribution, predominating in areas of greater friction, and affecting mainly both elbows, knees, buttocks, ankles, and may also affect the scalp and other parts of the body, and non-symmetrical occasionally. The lesions are vesicular-crusted and when flake off, they evolve to pigmented areas or achromic an intense burning, itchy and blistering rash. Despite its name, DH is neither related to nor caused by herpes virus: the name means that it is a skin inflammation having an appearance similar to herpes.

The age of onset is variable starting in children and adolescence but can also affect individuals of both sexes indistinctly at any age of their lives.

A fact that difficults its diagnosis is the relatively common presentation with atypical manifestations. Some patients may show erythema or severe pruritus alone, wheals of chronic urticaria, purpuric lesions resembling petechiae on hands and feet, palmo-plantar keratosis, leukocytoclastic vasculitis-like appearance, and/or lesions mimicking prurigo pigmentosa. DH may be confused with many different cutaneous lesions, such as atopic dermatitis, eczema, urticaria, scabies, impetigo, polymorphic erythema and other autoimmune blistering diseases.

DH is considered to be as "the coeliac disease of the skin". For this reason, the new guidelines of the European Society for Pediatric Gastroenterology, Hepatology and Nutrition for the diagnosis of coeliac disease conclude that its proven presence, by itself, confirms the diagnosis of coeliac disease. Nevertheless, duodenal biopsy is recommended in doubtful DH cases, or if there are suspected gastrointestinal complications, including lymphoma. People with DH have different degrees of intestinal involvement, ranging from milder mucosal lesions to the presence of villous atrophy.

The main and more efficacious treatment for DH is following a lifelong gluten-free diet, which produces the improvement of skin and gut lesions. Nevertheless, the skin lesions may take several months or even years to disappear. To calm itching, dapsone is often recommended as a temporary treatment, during the time it takes for the diet to work, but it has no effect on the gastrointestinal changes and may have important side effects.

Food intolerance is more chronic, less acute, less obvious in its presentation, and often more difficult to diagnose than a food allergy.

Symptoms of food intolerance vary greatly, and can be mistaken for the symptoms of a food allergy. While true allergies are associated with fast-acting immunoglobulin IgE responses, it can be difficult to determine the offending food causing a food intolerance because the response generally takes place over a prolonged period of time. Thus, the causative agent and the response are separated in time, and may not be obviously related. Food intolerance symptoms usually begin about half an hour after eating or drinking the food in question, but sometimes symptoms may be delayed by up to 48 hours.

Food intolerance can present with symptoms affecting the skin, respiratory tract, gastrointestinal tract (GIT) either individually or in combination. On the skin may include skin rashes, urticaria (hives), angioedema, dermatitis, and eczema. Respiratory tract symptoms can include nasal congestion, sinusitis, pharyngeal irritations, asthma and an unproductive cough. GIT symptoms include mouth ulcers, abdominal cramp, nausea, gas, intermittent diarrhea, constipation, irritable bowel syndrome (IBS),

and may include anaphylaxis.

Food intolerance has been found associated with irritable bowel syndrome and inflammatory bowel disease, chronic constipation, chronic hepatitis C infection, eczema, NSAID intolerance, respiratory complaints, including asthma, rhinitis and headache, functional dyspepsia, eosinophilic esophagitis

and ENT illnesses.

Food intolerance is a detrimental reaction, often delayed, to a food, beverage, food additive, or compound found in foods that produces symptoms in one or more body organs and systems, but generally refers to reactions other than food allergy. Food hypersensitivity is used to refer broadly to both food intolerances and food allergies.

Food allergies are immune reactions, typically an IgE reaction caused by the release of histamine but also encompassing non-IgE immune responses. This mechanism causes allergies to typically give immediate reaction (a few minutes to a few hours) to foods.

Food intolerances can be classified according to their mechanism. Intolerance can result from the absence of specific chemicals or enzymes needed to digest a food substance, as in hereditary fructose intolerance. It may be a result of an abnormality in the body's ability to absorb nutrients, as occurs in fructose malabsorption. Food intolerance reactions can occur to naturally occurring chemicals in foods, as in salicylate sensitivity. Drugs sourced from plants, such as aspirin, can also cause these kinds of reactions.