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 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.

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.

Food allergies develop more easily in people with the atopic syndrome, a very common combination of diseases: allergic rhinitis and conjunctivitis, eczema, and asthma. The syndrome has a strong inherited component; a family history of allergic diseases can be indicative of the atopic syndrome.

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.

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%.

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.

Influenza vaccines are created by injecting a live virus into fertilized chicken eggs. The viruses are harvested, killed and purified, but a residual amount of egg white protein remains. Each year, vaccines are created to provide protection against the flu viruses expected to be prevalent in the upcoming cold weather months. For the 2017-2018 flu season, the vaccines are described as IIV3 and IIV4 for resistance to the expected three or four viruses. For adults ages 18 and older there is also an option to receive recombinant flu vaccines (RIV3 or RIV4) which are grown on mammalian cell cultures instead of in eggs, and so are no risk for people with severe egg allergy. Recommendations are that for people with a history of mild egg allergy should receive any IIV or RIV vaccine. People with a more severe allergic reaction may also receive any IIV or RIV, but in an inpatient or outpatient medical setting, administered by a healthcare provider. People with a known severe allergic reaction to influenza vaccine (which could be egg protein or the gelatin or the neomycin components of the vaccine) should not receive a flu vaccine.

Each year the American Academy of Pediatrics (AAP) publishes recommendations for prevention and control of influenza in children. In the most recent guidelines, for 2016-2017, a change was made, that children with a history of egg allergy may receive the IIV3 or IIV4 vaccine without special precautions. It does, however, state that "Standard vaccination practice should include the ability to respond to acute hypersensitivity reactions." Prior to this, AAP recommended precautions based on egg allergy history: if no history, immunize; if a history of mild reaction, i.e., hives, immunize in a medical setting with healthcare professionals and resuscitative equipment available; if a history of severe reactions, refer to an allergist.

The measles and mumps parts of the "MMR vaccine" (for measles, mumps, and rubella) are cultured on chick embryo cell culture and contain trace amounts of egg protein. The amount of egg protein is lower than in influenza vaccines and the risk of an allergic reaction is much lower. One guideline stated that all infants and children should get the two MMR vaccinations, mentioning that "Studies on large numbers of egg-allergic children show there is no increased risk of severe allergic reactions to the vaccines." Another guideline recommended that if a child has a known medical history of severe anaphylaxis reaction to eggs, then the vaccination should be done in a hospital center, and the child be kept for observation for 60 minutes before being allowed to leave. The second guideline also stated that if there was a severe reaction to the first vaccination - which could have been to egg protein or the gelatin and neomycin components of the vaccine - the second is contraindicated.

Risk factors for drug allergies can be attributed to the drug itself or the characteristics of the patient. Drug-specific risk factors include the dose, route of administration, duration of treatment, repetitive exposure to the drug, and concurrent illnesses. Host risk factors include age, sex, atopy, specific genetic polymorphisms, and inherent predisposition to react to multiple unrelated drugs (multiple drug allergy syndrome).

A drug allergy is more likely to develop with large doses and extended exposure.

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.

Reactions to chemical components of the diet are more common than true food allergies. Although, there is no evidence to support this. They are caused by various organic chemicals occurring naturally in a wide variety of foods, both of animal and vegetable origin more often than to food additives, preservatives, colourings and flavourings, such as sulfites or dyes.

Both natural and artificial ingredients may cause adverse reactions in sensitive people if consumed in sufficient amount, the degree of sensitivity varying between individuals.

Pharmacological responses to naturally occurring compounds in food, or chemical intolerance, can occur in individuals from both allergic and non-allergic family backgrounds. Symptoms may begin at any age, and may develop quickly or slowly. Triggers may range from a viral infection or illness to environmental chemical exposure. It occurs more commonly in women, which may be because of hormone differences, as many food chemicals mimic hormones.

A deficiency in digestive enzymes can also cause some types of food intolerances. Lactose intolerance is a result of the body not producing sufficient lactase to digest the lactose in milk; dairy foods which are lower in lactose, such as cheese, are less likely to trigger a reaction in this case. Another carbohydrate intolerance caused by enzyme deficiency is hereditary fructose intolerance.

Celiac disease, an autoimmune disorder caused by an immune response to the protein gluten, results in gluten intolerance and can lead to temporary lactose intolerance.

The most widely distributed naturally occurring food chemical capable of provoking reactions is salicylate, although tartrazine and benzoic acid are well recognised in susceptible individuals. Benzoates and salicylates occur naturally in many foods, including fruits, juices, vegetables, spices, herbs, nuts, tea, wines, and coffee. Salicylate sensitivity causes reactions to not only aspirin and NSAIDs but also foods in which salicylates naturally occur, such as cherries.

Other natural chemicals which commonly cause reactions and cross reactivity include amines, nitrates, sulphites and some antioxidants. Chemicals involved in aroma and flavour are often suspect.

The classification or avoidance of foods based on botanical families bears no relationship to their chemical content and is not relevant in the management of food intolerance.

Salicylate-containing foods include apples, citrus fruits, strawberries, tomatoes, and wine, while reactions to chocolate, cheese, bananas, avocado, tomato or wine point to amines as the likely food chemical. Thus, exclusion of single foods does not necessarily identify the chemical responsible as several chemicals can be present in a food, the patient may be sensitive to multiple food chemicals and reaction more likely to occur when foods containing the triggering substance are eaten in a combined quantity that exceeds the patient's sensitivity thresholds. People with food sensitivities have different sensitivity thresholds, and so more sensitive people will react to much smaller amounts of the substance.

Food intolerance are all other adverse reactions to food. Subgroups include enzymatic (e.g. lactose intolerance due to lactase deficiency), pharmacological (e.g. reactions against biogenic amines, histamine intolerance), and undefined food intolerance (e.g. against some food additives).

Food intolerances can be caused by enzymatic defects in the digestive system, can also result from pharmacological effects of vasoactive amines present in foods (e.g. Histamine), among other metabolic, pharmacological and digestive abnormalities.

Allergies and intolerances to a food group may coexist with separate pathologies; for example, cow's milk allergy (CMA) and lactose intolerance are two distinct pathologies.

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.

Some examples:

- Allergic asthma

- Allergic conjunctivitis

- Allergic rhinitis ("hay fever")

- Anaphylaxis

- Angioedema

- Urticaria (hives)

- Eosinophilia

- Penicillin allergy

- Cephalosporin allergy

- Food allergy

- Sweet itch

When a medication causes an allergic reaction, it is called an allergen. The following is a short list of the most common drug allergens:

- Antibiotics

- Penicillin

- Sulfa drugs

- Tetracycline

- Analgesics

- Codeine

- Non-steroidal anti-inflammatory drugs (NSAIDs)

- Antiseizure

- Phenytoin

- Carbamazepine

Treatment usually involves adrenaline (epinephrine), antihistamines, and corticosteroids.

If the entire body is involved, then anaphylaxis can take place, which is an acute, systemic reaction that can prove fatal.

The majority of individuals who receive a sting from an insect experience local reactions. It is estimated that 5-10% of individuals will experience a generalized systemic reaction that can involve symptoms ranging from hives to wheezing and even anaphylaxis. In the United States approximately 40 people die each year from anaphylaxis due to stinging insect allergy. Potentially life-threatening reactions occur in 3% of adults and 0.4–0.8% of children.

The imbalance in histamine intolerance is between the synthesis and selective release of histamine from certain granulocytes (i.e., mast cells and basophils), versus the breakdown of histamine by the enzymes which metabolize it, such as diamine oxidase (DAO) and histamine N-methyltransferase (HNMT).

In contrast, allergic reactions involving an immediate allergic response to an allergen are caused by anaphylactic degranulation, which is the abrupt and explosive release of "pre-formed mediators", including histamine, from mast cells and basophils throughout the body.

The most common food allergies in adults are shellfish and nuts. The most common food allergies in children are shellfish, nuts, eggs, wheat, and soy. One study showed Balsam of Peru, which is in many processed foods, to be the most common cause of immediate contact urticaria. A less common cause is exposure to certain bacteria, such as "Streptococcus" species or possibly "Helicobacter pylori".

Drugs that have caused allergic reactions evidenced as hives include codeine, dextroamphetamine, aspirin, ibuprofen, penicillin, clotrimazole, trichazole, sulfonamides, anticonvulsants, cefaclor, piracetam, vaccines, and antidiabetic drugs. The antidiabetic sulphonylurea glimepiride, in particular, has been documented to induce allergic reactions manifesting as hives. Drug-induced hives has been known to have an effect on severe cardiorespiratory failure.

Histamine intolerance, sometimes called histaminosis, is an over-accumulation of histamine in the human body. Histamine intolerance is sometimes informally called an allergy; however, the intolerance is technically caused by the gradual accumulation of extracellular histamine due to an imbalance.

Roughly 1% of the population suffers from histamine intolerance; of those, 80% are middle-aged.

Allergic conjunctivitis occurs more frequently among those with allergic conditions, with the symptoms having a seasonal correlation.

Allergic conjunctivitis is a frequent condition as it is estimated to affect 20 percent of the population on an annual basis and approximately one-half of these people have a personal or family history of atopy.

Giant papillary conjunctivitis accounts for 0.5–1.0% of eye disease in most countries.

The Allergic Alсоhоl from the original on 30 April 2012. Retrieved 2010-04-08.

The cause of allergic conjunctivitis is an allergic reaction of the body's immune system to an allergen. Allergic conjunctivitis is common in people who have other signs of allergic disease such as hay fever, asthma and eczema.

Among the most common allergens that cause conjunctivitis are:

- Pollen from trees, grass and ragweed

- Animal skin and secretions such as saliva

- Perfumes

- Cosmetics

- Skin medicines

- Air pollution

- Smoke

- Dust mites

- Balsam of Peru (used in food and drink for flavoring, in perfumes and toiletries for fragrance, and in medicine and pharmaceutical items for healing properties)

- Eye drops

Most cases of seasonal conjunctivitis are due to pollen and occur in the hay fever season, grass pollens in early summer and various other pollens and moulds may cause symptoms later in the summer.

An important salicylate drug is aspirin, which has a long history. Aspirin intolerance was widely known by 1975, when the understanding began to emerge that it is a pharmacological reaction, not an allergy.

Salicylate sensitivity, also known as salicylate intolerance, is any adverse effect that occurs when a usual amount of salicylate is ingested. People with salicylate intolerance are unable to consume a normal amount of salicylate without adverse effects.

Salicylate sensitivity differs from salicylism, which occurs when an individual takes an overdose of salicylates. Salicylate overdose can occur in people without salicylate sensitivity, and can be deadly if untreated. For more information, see aspirin poisoning.

Salicylates are derivatives of salicylic acid that occur naturally in plants and serve as a natural immune hormone and preservative, protecting the plants against diseases, insects, fungi, and harmful bacteria. Salicylates can also be found in many medications, perfumes and preservatives. Both natural and synthetic salicylates can cause health problems in anyone when consumed in large doses. But for those who are salicylate intolerant, even small doses of salicylate can cause adverse reactions.