The majority of children outgrow egg allergy. One review reported that 70% of children will outgrow this allergy by 16 years. In subsequently published longitudinal studies, one reported that for 140 infants who had challenge-confirmed egg allergy, 44% had resolved by two years. A second reported that for 203 infants with confirmed IgE-mediated egg allergy, 45% resolved by two years of age, 66% by four years, and 71% by six years. Children will be able to tolerate eggs as an ingredient in baked goods and well-cooked eggs sooner than under-cooked eggs. Resolution was more likely if baseline serum IgE was lower, and if the baseline symptoms did not include anaphylaxis.

When infants consume peanut proteins while 4 to 11 months old, the risk of developing peanut allergy before the age of 5 years decreases by 11-25%, specifically in children with higher allergy risk via their parents with peanut allergy. From these results, the American Academy of Pediatrics rescinded their recommendation to delay exposure to peanuts in children, also stating there is no reason to avoid peanuts during pregnancy or breastfeeding.

There is conflicting evidence on whether maternal diet during pregnancy has any effect on development of allergies due to a lack of good studies. A 2010 systematic review of clinical research indicated that there is insufficient evidence for whether maternal peanut exposure, or early consumption of peanuts by children, affects sensitivity for peanut allergy.

Milk allergy typically presents in the first year of life. The majority of children outgrow milk allergy by the age of ten years. One large clinical trial reported resolutions of 19% by age 4 years, 42% by age 8 years, 64% by age 12 years, and 79% by 16 years. Children are be able to tolerate milk as an ingredient in baked goods relative to liquid milk. Resolution was more likely if baseline serum IgE was lower, or if IgE-mediated allergy was absent so that all that was present was cell-mediated, non-IgE allergy.

People with confirmed cow's milk allergy may also demonstrate an allergic response to beef, moreso to rare beef versus well-cooked beef. The offending protein appears to be bovine serum albumin. This is not the same beef allergy that is seen primarily in the southeastern United States, triggered by being bitten by a Lone Star tick.

Milk allergy has consequences. In a U.S. government diet and health surveys conducted in 2007-2010, 6,189 children ages 2-17 years were assessed. For those classified as cow's milk allergic at the time of the survey, mean weight, height and body-mass index were significantly lower than their non-allergic peers. This was not true for children with other food allergies. Diet assessment showed a significant 23% reduction of calcium intake and near-significant trends for lower vitamin D and total calorie intake.

The most common food allergens account for about 90% of all allergic reactions; in adults they include shellfish, peanuts, tree nuts, fish, and egg. In children, they include milk, eggs, peanuts, and tree nuts. Six to 8% of children under the age of three have food allergies and nearly 4% of adults have food allergies.

For reasons not entirely understood, the diagnosis of food allergies has apparently become more common in Western nations recently. In the United States, food allergy affects as many as 5% of infants less than three years of age and 3% to 4% of adults. A similar prevalence is found in Canada.

About 75% of children who have allergies to milk protein are able to tolerate baked-in milk products, i.e., muffins, cookies, cake, and hydrolyzed formulas.

About 50% of children with allergies to milk, egg, soy, peanuts, tree nuts, and wheat will outgrow their allergy by the age of 6. Those who are still allergic by the age of 12 or so have less than an 8% chance of outgrowing the allergy.

Peanut and tree nut allergies are less likely to be outgrown, although evidence now shows that about 20% of those with peanut allergies and 9% of those with tree nut allergies will outgrow them.

In Japan, allergy to buckwheat flour, used for soba noodles, is more common than peanuts, tree nuts or foods made from soy beans.

Corn allergy may also be prevalent in many populations, although it may be difficult to recognize in areas such as the United States and Canada where corn derivatives are common in the food supply.

Each home contains possible allergens that can develop into allergies after exposure to:

- Dust mites

- Dogs and cats

- Other furry pets

- Cockroaches

- Mice and rats)

- Plants

- Mold

Vitamin D deficiency at the time of birth and exposure to egg white, milk, peanut, walnut, soy, shrimp, cod fish, and wheat makes a child more susceptible to allergies. Soy-based infant formula is associated with allergies in infants.

A child's allergy is an immune system reaction. The child is reacting to a specific substance, or allergen. The immune system of a child responds to the invading allergen by releasing histamine and other chemicals that typically trigger symptoms in the nose, lungs, throat, sinuses, ears, eyes, skin, or stomach lining. In some children, allergies can also trigger symptoms of asthma—a disease that causes wheezing or difficulty breathing. If a child has allergies and asthma, controlling the allergies is important because the lack of treatment may make the allergies worse. Compounds such as phthalates are associated with asthma in children. Asthma in children is associated with exposure to indoor allergens. in early childhood may prevent the development of asthma, but exposure at an older age may provoke bronchoconstriction. Use of antibiotics in early life has been linked to the development of asthma. Exposure to indoor volatile organic compounds may be a trigger for asthma; formaldehyde exposure, for example, has a positive association.

Contact sensitivity, atopic dermatitis, eczema, and urticaria appear to be related phenomena, the cause of which is generally believed to be the hydrophobic prolamin components of certain Triticeae, Aveneae cultivars. In wheat one of these proteins is ω-gliadin (Gli-B1 gene product). A study of mothers and infants on an allergen-free diet demonstrated that these conditions can be avoided if wheat sensitive cohort in the population avoid wheat in the first year of life. As with exercise induced anaphylaxis aspirin (also: tartrazine, sodium benzoate, sodium glutamate (MSG), sodium metabisulfite, tyramine) may be sensitizing factors for reactivity. Studies of the wheat-dependent exercise induced anaphylaxis demonstrate that atopy and EIA can be triggered from the ingestion of that aspirin and probably NSAIDs allow the entry of wheat proteins into the blood, where IgE reacts within allergens in the dermal tissues. Some individuals may be so sensitive that low dose aspirin therapy can increase risk for both atopy and WDEIA.

Wheat allergies were also common with contact dermatitis. A primary cause was the donning agent used for latex gloves prior to the 1990s, however most gloves now use protein free starch as donning agents.

Alpha-gal allergies develop after a person has been bitten by the lone star tick in the United States, the European castor bean tick, and the paralysis tick in Australia. Alpha-gal is not naturally present in apes and humans, but is in all other mammals. If a tick feeds on another mammal, the alpha-gal will remain in its alimentary tract. The tick will then inject the alpha-gal into a person's skin, which in turn will cause the immune system to release a flood of IgE antibodies to fight off the foreign carbohydrate. Researchers still do not know which specific component of tick saliva causes the reaction.

A 2012 preliminary study found unexpectedly high rates of alpha-gal allergies in the Western and North Central parts of the United States, which suggests that the allergy may be spread by unknown tick species. Examples of alpha-gal allergies were even present in Hawaii, where none of the ticks identified with the allergies live. Human factors were suggested but no specific examples were provided.

Alpha-gal is present in the anti-cancer drug cetuximab, as well as the IV fluid replacements Gelofusine and Haemaccel. Blood thinners derived from porcine intestine and replacement heart valves derived from porcine tissue may also contain alpha-gal.

There has been at least one instance of a man with an alpha-gal allergy going into anaphylaxis after receiving a heart valve transplant. Some researchers have suggested that the alpha-gal which is prevalent in pig's tissue and used for xenografts may contribute to organ rejection.

Incidence and prevalence are terms commonly used in describing disease epidemiology. Incidence is newly diagnosed cases, which can be expressed as new cases per year per million people. Prevalence is the number of cases alive, expressible as existing cases per million people during a period of time. Milk allergies are usually observed in infants and young children, and often disappear with age (see Prognosis), so prevalence of egg allergy may be expressed as a percentage of children under a set age. Milk allergy affects between 2% and 3% of infants in developed countries. This estimate is for antibody-based allergy; prevalence of allergy based on cellular immunity is unknown.

For all age groups, a review of fifty studies conducted in Europe estimated 6.0% for self-reported milk allergy and 0.6% for confirmed. National survey data in the United States collected 2005-2006 showed that from age six and older, the prevalence of serum IgE confirmed milk allergy was under 0.4%.

Allergies to a specific pollen are usually associated with OAS reactions to other certain foods. For instance, an allergy to ragweed is associated with OAS reactions to banana, watermelon, cantaloupe, honeydew, zucchini, and cucumber. This does not mean that all sufferers of an allergy to ragweed will experience adverse effects from all or even any of these foods. Reactions may be associated with one type of food, with new reactions to other foods developing later. However, reaction to one or more foods in any given category does not necessarily mean a person is allergic to all foods in that group.

In countries in North America and western Europe, where use of cow's milk based infant formula is common, chicken egg allergy is the second most common food allergy in infants and young children after cow's milk. However, in Japan, egg allergy is first and cow's milk second, followed by wheat and then the other common allergenic foods. A review from South Africa reported egg and peanut as the two most common allergenic foods.

Incidence and prevalence are terms commonly used in describing disease epidemiology. Incidence is newly diagnosed cases, which can be expressed as new cases per year per million people. Prevalence is the number of cases alive, expressible as existing cases per million people during a period of time. Egg allergies are usually observed in infants and young children, and often disappear with age (see Prognosis), so prevalence of egg allergy may be expressed as a percentage of children under a set age. One review estimates that in North American and western European populations the prevalence of egg allergy in children under the age of five years is 1.8-2.0%. A second described the range in young children as 0.5-2.5%. Although the majority of children develop tolerance as they age into school age years, for roughly one-third the allergy persists into adulthood. Strong predictors for adult-persistent allergy are anaphylactic symptoms as a child, high egg-specific serum IgE, robust response to the skin prick test and absence of tolerance to egg-containing baked foods. Self-reported allergy prevalence is always higher than food-challenge confirmed allergy.

For all age groups, a review of fifty studies conducted in Europe estimated 2.5% for self-reported egg allergy and 0.2% for confirmed. National survey data in the United States collected in 2005 and 2006 showed that from age six and older, the prevalence of serum IgE confirmed egg allergy was under 0.2%.

Adult-onset of egg allergy is rare, but there is confirmation of cases. Some were described as having started in late teenage years; another group were workers in the baking industry who were exposed to powdered egg dust.

For those allergic to fruits, cooking may help reduce or eliminate the reaction to some fruits.

People with this allergy might not necessarily be allergic to citrus fruits.

OAS produces symptoms when an affected person eats certain fruits, vegetables, and nuts. Some individuals may only show allergy to only one particular food, and others may show an allergic response to many foods.

Individuals with an allergy to tree pollen may develop OAS to a variety of foods. While the tree pollen allergy has been worked out, the grass pollen is not well understood. Furthermore, some individuals have severe reactions to certain fruits and vegetables that do not fall into any particular allergy category. In recent years, it has also become apparent that when tropical foods initiate OAS, allergy to latex may be the underlying cause.

Because the allergenic proteins associated with OAS are usually destroyed by cooking, most reactions are caused by eating raw foods. The main exceptions to this are celery and nuts, which may cause reactions even after being cooked.

There appears to be an association of autoimmune rheumatoid arthritis (ARA) both with GSE and gluten allergies. ARA in GSE/CD may be secondary to tTG autoimmunity. In a recent study in Turkey, 8 of 20 ARA patients had wheat reactivities on the RAST tests. When this allergic food and all other patient specific RAST+ foods were removed half of the patients had improved ARA by serological markers. In patients with wheat allergies, rye was effectively substituted. This may indicate that some proportion of RA in GSE/CD is due to downstream effects of allergic responses. In addition, cross-reactive anti-beef-collagen antibodies (IgG) may explain some "rheumatoid arthritis" (RA) incidences.

There are many different types of fruits that people have been shown to react allergically such as mangoes and bananas. Some foods are clearly more allergenic than others. In adults, peanuts, tree nuts, finned fish, crustaceans, fruit, and vegetables account for 85% of the food-allergic reactions(O'Neil, Zanovec and Nickla).

People suffering from allergies may suffer from a hypersensitivity to the allergic food, which is what causes the allergic reaction. Most fruit allergies are oral syndrome allergies because they are consumed but may also be an external allergy if the fruit touches the skin.

A tree nut allergy is a hypersensitivity to dietary substances from tree nuts and edible tree seeds causing an overreaction of the immune system which may lead to severe physical symptoms. Tree nuts include, but are not limited to, almonds, Brazil nuts, cashews, chestnuts, filberts/hazelnuts, macadamia nuts, pecans, pistachios, pine nuts, shea nuts and walnuts.

Tree nut allergies are distinct from peanut allergy, as peanuts are legumes, whereas a tree nut is a hard-shelled nut.

An Institute of Medicine report says that food proteins contained in vaccines, such as gelatin, milk, or egg can cause sensitization (development of allergy) in vaccine recipients, to those food items.

Although genetic factors govern susceptibility to atopic disease, increases in atopy have occurred within too short a time frame to be explained by a genetic change in the population, thus pointing to environmental or lifestyle changes. Several hypotheses have been identified to explain this increased rate; increased exposure to perennial allergens due to housing changes and increasing time spent indoors, and changes in cleanliness or hygiene that have resulted in the decreased activation of a common immune control mechanism, coupled with dietary changes, obesity and decline in physical exercise. The hygiene hypothesis maintains that high living standards and hygienic conditions exposes children to fewer infections. It is thought that reduced bacterial and viral infections early in life direct the maturing immune system away from T1 type responses, leading to unrestrained T2 responses that allow for an increase in allergy.

Changes in rates and types of infection alone however, have been unable to explain the observed increase in allergic disease, and recent evidence has focused attention on the importance of the gastrointestinal microbial environment. Evidence has shown that exposure to food and fecal-oral pathogens, such as hepatitis A, "Toxoplasma gondii", and "Helicobacter pylori" (which also tend to be more prevalent in developing countries), can reduce the overall risk of atopy by more than 60%, and an increased rate of parasitic infections has been associated with a decreased prevalence of asthma. It is speculated that these infections exert their effect by critically altering T1/T2 regulation. Important elements of newer hygiene hypotheses also include exposure to endotoxins, exposure to pets and growing up on a farm.

Within the workplace, individuals may be exposed to significant amounts of nickel, airborne from the combustion of fossil fuels, or from contact with tools that are nickel-plated. Historically, workplaces where prolonged contact with soluble nickel has been high, have shown high risks for allergic contact nickel dermatitis. For example, nickel dermatitis was common in the past among nickel platers. Due to improved industrial and personal hygiene practices, however, over the past several decades, reports of nickel sensitivity in workplaces, such as the electroplating industry, have been sparse. In the workplace, exposure reduction includes personal protection equipment and other risk management measures.

Nickel allergy results in a skin response (rash) after the skin comes in direct and sustained contact with any item which releases a large amount of free nickel from its surface. The skin reaction can occur at the site of contact, or sometimes spread beyond to the rest of the body. Cutaneous exposure can cause localized erythematous, pruritic, vesicular, and scaly patches. Ingestion of nickel may cause a systemic reaction, that will affect a larger skin surface. Examples of systemic reactions can include hand dermatitis, baboon syndrome, or generalized eczematous reactions.

Risk factors for allergy can be placed in two general categories, namely host and environmental factors. Host factors include heredity, sex, race, and age, with heredity being by far the most significant. However, there have been recent increases in the incidence of allergic disorders that cannot be explained by genetic factors alone. Four major environmental candidates are alterations in exposure to infectious diseases during early childhood, environmental pollution, allergen levels, and dietary changes.

Unlike other food allergies, rice allergy is relatively uncommon. It has been reported worldwide but mostly in China, Japan or Korea. Because rice is a major food in Asia, people from Asia are exposed to higher allergy risk than people from other areas.

People with tree nut allergy are seldom allergic to just one type of nut, and are therefore usually advised to avoid all tree nuts, even though an individual may not be allergic to the nuts of all species of trees.

Someone allergic to walnuts or pecans may not have an allergy to cashews or pistachios, because the two groups are only distantly related and do not necessarily share related allergenic proteins. The severity of the allergy varies from person to person, and exposure can increase sensitization. For those with a milder form of the allergy, a reaction which makes the throat feel like cotton may occur. Subjects allergic to tree nut can experience asthma, skin rashes, itchy throat, swollen eyes. The most severe reaction can lead to anaphylaxis and sensitive subjects may need to carry with them at all times disposable adrenaline injectors prescribed by their GP. Less severe reaction can be dealt with by assuming antihistamines tablet. The raw nut protein usually causes a more severe reaction than the oil, and extra roasting or processing can reduce the allergic reaction. Those diagnosed with anaphylaxis will have a more immediate mast cell reaction and be required to avoid all exposure to any allergen-containing products or byproducts, regardless of processing, as they are prone to even greater sensitivity. An allergy test or food challenge may be performed at an allergy clinic to determine the exact allergens. New immunotherapy treatments are being developed for tree nut allergy.

This allergy tends to be lifelong; recent studies have shown that only about 9% of children outgrow their tree nut allergy.

Hazelnut has been used as a model tree nut in the study of tree nut allergies.

Allergens that are airborne survive for months or even years by themselves, hence removing anything that can trap and hold the allergens (carpet, rugs, pillows) and cleaning regularly and thoroughly with HEPA filters and electrostatic air purifier systems reduces risk. Frequent hand washing, especially after handling the cat, and washing hands prior to touching eyes, nose, or mouth, and limiting the cat's access to certain rooms, such as the bedroom or other rooms where much time is spent, may also reduce allergic reactions.