Allergies

Allergies, also known as allergic diseases, are a number of conditions caused by of the  to typically harmless substances in the environment. These diseases include, , , , and. Symptoms may include, an itchy rash, , a , , or swelling. and are separate conditions.

Common s include and certain food. Metals and other substances may also cause problems. Food, s, and medications are common causes of severe reactions. Their development is due to both genetic and environmental factors. The underlying mechanism involves (IgE), part of the body's immune system, binding to an allergen and then to  on s or s where it triggers the release of inflammatory chemicals such as. Diagnosis is typically based on a person's. Further testing of the or blood may be useful in certain cases. Positive tests, however, may not mean there is a significant allergy to the substance in question.

Early exposure to potential allergens may be protective. Treatments for allergies include avoiding known allergens and the use of medications such as and. In severe reactions injectable (epinephrine) is recommended. , which gradually exposes people to larger and larger amounts of allergen, is useful for some types of allergies such as hay fever and reactions to insect bites. Its use in food allergies is unclear.

Allergies are common. In the developed world, about 20% of people are affected by, about 6% of people have at least one food allergy, and about 20% have at some point in time. Depending on the country about 1–18% of people have asthma. Anaphylaxis occurs in between 0.05–2% of people. Rates of many allergic diseases appear to be increasing. The word "allergy" was first used by in 1906.

Signs and symptoms
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,, 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 in the s,, coughing, and wheezing.

Aside from these ambient allergens, allergic reactions can result from s,, and reactions to s like and s such as. Symptoms of food allergy include, , vomiting, , y skin, and. Food allergies rarely cause (asthmatic) reactions, or. Insect stings, food,, and certain medicines may produce a systemic allergic response that is also called ; multiple organ systems can be affected, including the , the , and the. Depending on the rate of severity, anaphylaxis can include skin reactions, bronchoconstriction,, , , and. This type of reaction can be triggered suddenly, or the onset can be delayed. The nature of is such that the reaction can seem to be subsiding, but may recur throughout a period of time.

Skin
Substances that come into contact with the skin, such as, are also common causes of allergic reactions, known as or eczema. Skin allergies frequently cause rashes, or swelling and inflammation within the skin, in what is known as a " and flare" reaction characteristic of hives and angioedema.

With insect stings a large local reaction may occur (an area of skin redness greater than 10 cm in size). It can last one to two days. This reaction may also occur after.

Cause
Risk factors for allergy can be placed in two general categories, namely and  factors. Host factors include, , , 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 s during early childhood, environmental, allergen levels, and changes.

Foods
A wide variety of foods can cause allergic reactions, but 90% of allergic responses to foods are caused by cow's, , , , s, , , and. Other, affecting less than 1 person per 10,000 population, may be considered "rare". The use of hydrolysed milk versus standard milk baby formula does not appear to change the risk.

The most common food allergy in the US population is a sensitivity to. Although peanut allergies are notorious for their severity, peanut allergies are not the most common food allergy in adults or children. Severe or life-threatening reactions may be triggered by other allergens, and are more common when combined with asthma.

Rates of allergies differ between adults and children. allergies can sometimes be outgrown by children. Egg allergies affect one to two percent of children but are outgrown by about two-thirds of children by the age of 5. The sensitivity is usually to proteins in the white, rather than the.

Milk-protein allergies are most common in children. Approximately 60% of milk-protein reactions are -mediated, with the remaining usually attributable to. Some people are unable to tolerate milk from goats or sheep as well as from cows, and many are also unable to tolerate products such as cheese. Roughly 10% of children with a milk allergy will have a reaction to. Beef contains a small amount of protein that is present in cow's milk. , a common reaction to milk, is not a form of allergy at all, but rather due to the absence of an in the.

Those with allergies may be allergic to one or to many tree nuts, including pecans, pistachios, pine nuts, and walnuts. Also, including and s, contain oils in which protein is present, which may elicit an allergic reaction.

Allergens can be transferred from one food to another through ; however genetic modification can also remove allergens. Little research has been done on the natural variation of allergen concentrations in the unmodified crops.

Latex
can trigger an IgE-mediated cutaneous, respiratory, and systemic reaction. The prevalence of latex allergy in the general population is believed to be less than one percent. In a hospital study, 1 in 800 surgical patients (0.125 percent) reported latex sensitivity, although the sensitivity among healthcare workers is higher, between seven and ten percent. Researchers attribute this higher level to the exposure of healthcare workers to areas with significant airborne latex allergens, such as operating rooms, intensive-care units, and dental suites. These latex-rich environments may sensitize healthcare workers who regularly inhale allergenic proteins.

The most prevalent response to latex is an allergic contact dermatitis, a delayed hypersensitive reaction appearing as dry, crusted lesions. This reaction usually lasts 48–96 hours. Sweating or rubbing the area under the glove aggravates the lesions, possibly leading to ulcerations. reactions occur most often in sensitive patients who have been exposed to a surgeon's latex gloves during abdominal surgery, but other exposures, such as dental procedures, can also produce systemic reactions.

Latex and banana sensitivity may cross-react. Furthermore, those with latex allergy may also have sensitivities to avocado, kiwifruit, and chestnut. These people often have itching and local. Only occasionally have these food-induced allergies induced systemic responses. Researchers suspect that the cross-reactivity of latex with banana, avocado, kiwifruit, and chestnut occurs because latex proteins are structurally with some other plant proteins.

Medications
About 10% of people report that they are allergic to ; however, 90% turn out not to be. Serious allergies only occur in about 0.03%.

Insect stings
Typically, which generate allergic responses are either stinging insects (,,  and ) or biting insects. Stinging insects inject venom into their victims, whilst biting insects normally introduce.

Toxins interacting with proteins
Another non-food protein reaction,, originates after contact with , , , or. , which is not itself a protein, acts as a and chemically reacts with, binds to, and changes the shape of s on exposed skin cells. The immune system does not recognize the affected cells as normal parts of the body, causing a - mediated. Of these poisonous plants, sumac is the most virulent. The resulting dermatological response to the reaction between urushiol and membrane proteins includes redness, swelling, s,, s, and streaking.

Estimates vary on the percentage of the population that will have an immune system response. Approximately 25 percent of the population will have a strong allergic response to urushiol. In general, approximately 80 percent to 90 percent of adults will develop a rash if they are exposed to .0050 mg of purified urushiol, but some people are so sensitive that it takes only a molecular trace on the skin to initiate an allergic reaction.

Genetics
Allergic diseases are strongly : are likely to have the same allergic diseases about 70% of the time; the same allergy occurs about 40% of the time in. Allergic parents are more likely to have allergic children, and those children's allergies are likely to be more severe than those in children of non-allergic parents. Some allergies, however, are not consistent along ; parents who are allergic to s may have children who are allergic to. It seems that the likelihood of developing allergies is and related to an irregularity in the immune system, but the specific  is not.

The risk of allergic and the development of allergies varies with age, with young children most at risk. Several studies have shown that IgE levels are highest in childhood and fall rapidly between the ages of 10 and 30 years. The peak prevalence of hay fever is highest in children and young adults and the incidence of asthma is highest in children under 10.

Overall, boys have a higher risk of developing allergies than girls, although for some diseases, namely asthma in young adults, females are more likely to be affected. These differences between the sexes tend to decrease in adulthood.

may play a role in some allergies; however, racial factors have been difficult to separate from environmental influences and changes due to. It has been suggested that different are responsible for asthma, to be specific, in people of, , , and African origins.

Hygiene hypothesis
Allergic diseases are caused by inappropriate immunological responses to harmless driven by a -mediated immune response. Many and es elicit a -mediated immune response, which down-regulates TH2 responses. The first proposed mechanism of action of the hygiene hypothesis was that insufficient stimulation of the TH1 arm of the immune system leads to an overactive TH2 arm, which in turn leads to allergic disease. In other words, individuals living in too sterile an environment are not exposed to enough pathogens to keep the immune system busy. Since our bodies evolved to deal with a certain level of such pathogens, when they are not exposed to this level, the immune system will attack harmless antigens and thus normally benign microbial objects—like pollen—will trigger an immune response.

The hygiene hypothesis was developed to explain the observation that and, both allergic diseases, were less common in children from larger families, which were, it is presumed, exposed to more infectious agents through their siblings, than in children from families with only one child. The hygiene hypothesis has been extensively investigated by and  and has become an important theoretical framework for the study of allergic disorders. It is used to explain the increase in allergic diseases that have been seen since, and the higher incidence of allergic diseases in more developed countries. The hygiene hypothesis has now expanded to include exposure to symbiotic bacteria and parasites as important modulators of immune system development, along with infectious agents.

Epidemiological data support the hygiene hypothesis. Studies have shown that various immunological and autoimmune diseases are much less common in the developing world than the industrialized world and that immigrants to the industrialized world from the developing world increasingly develop immunological disorders in relation to the length of time since arrival in the industrialized world. Longitudinal studies in the third world demonstrate an increase in immunological disorders as a country grows more affluent and, it is presumed, cleaner. The use of antibiotics in the first year of life has been linked to asthma and other allergic diseases. The use of antibacterial cleaning products has also been associated with higher incidence of, as has birth by rather than vaginal birth.

Stress
Chronic can aggravate allergic conditions. This has been attributed to a T helper 2 (TH2)-predominant response driven by suppression of by both the  and the. Stress management in highly susceptible individuals may improve symptoms.

Other environmental factors
There are differences between countries in the number of individuals within a population having allergies. Allergic diseases are more common in countries than in countries that are more traditional or, and there is a higher rate of allergic disease in  populations versus  populations, although these differences are becoming less defined.

Alterations in exposure to s is another plausible explanation, at present, for the increase in. Endotoxin exposure reduces release of inflammatory s such as, , , and from white blood cells  that circulate in the. Certain microbe-sensing s, known as s, found on the surface of cells in the body are also thought to be involved in these processes.

Gutworms and similar parasites are present in untreated drinking water in developing countries, and were present in the water of developed countries until the routine and purification of drinking water supplies. Recent research has shown that some common s, such as (e.g., s), secrete chemicals into the gut wall (and, hence, the bloodstream) that  the immune system and prevent the body from attacking the parasite. This gives rise to a new slant on the hygiene hypothesis theory—that of humans and parasites has led to an immune system that functions correctly only in the presence of the parasites. Without them, the immune system becomes unbalanced and oversensitive. In particular, research suggests that allergies may coincide with the delayed establishment of in s. However, the research to support this theory is conflicting, with some studies performed in China and  showing an increase in allergy in people infected with intestinal worms. Clinical trials have been initiated to test the effectiveness of certain worms in treating some allergies. It may be that the term 'parasite' could turn out to be inappropriate, and in fact a hitherto unsuspected is at work. For more information on this topic, see.

Acute response
In the early stages of allergy, a type I hypersensitivity reaction against an allergen encountered for the first time and presented by a professional causes a response in a type of immune cell called a ; a subset of s that produce a  called  (IL-4). These TH2 cells interact with other called s, whose role is production of antibodies. Coupled with signals provided by IL-4, this interaction stimulates the B cell to begin production of a large amount of a particular type of antibody known as IgE. Secreted IgE circulates in the blood and binds to an IgE-specific receptor (a kind of called ) on the surface of other kinds of immune cells called s and s, which are both involved in the acute inflammatory response. The IgE-coated cells, at this stage, are sensitized to the allergen.

If later exposure to the same allergen occurs, the allergen can bind to the IgE molecules held on the surface of the mast cells or basophils. Cross-linking of the IgE and Fc receptors occurs when more than one IgE-receptor complex interacts with the same allergenic molecule, and activates the sensitized cell. Activated mast cells and basophils undergo a process called, during which they release and other inflammatory chemical mediators (s, s, s, and s) from their  into the surrounding tissue causing several systemic effects, such as ,  secretion,  stimulation, and  contraction. This results in, itchiness, dyspnea, and. Depending on the individual, allergen, and mode of introduction, the symptoms can be system-wide (classical anaphylaxis), or localized to particular body systems; asthma is localized to the respiratory system and eczema is localized to the.

Late-phase response
After the chemical mediators of the acute response subside, late-phase responses can often occur. This is due to the migration of other s such as s, s, s and s to the initial site. The reaction is usually seen 2–24 hours after the original reaction. Cytokines from mast cells may play a role in the persistence of long-term effects. Late-phase responses seen in are slightly different from those seen in other allergic responses, although they are still caused by release of mediators from eosinophils and are still dependent on activity of TH2 cells.

Allergic contact dermatitis
Although is termed an "allergic" reaction (which usually refers to type I hypersensitivity), its pathophysiology actually involves a reaction that more correctly corresponds to a  reaction. In type IV hypersensitivity, there is activation of certain types of (CD8+) that destroy target cells on contact, as well as activated s that produce  s.

Diagnosis
Effective management of allergic diseases relies on the ability to make an accurate diagnosis. Allergy testing can help confirm or rule out allergies. Correct diagnosis, counseling, and avoidance advice based on valid allergy test results reduces the incidence of symptoms and need for medications, and improves quality of life. To assess the presence of allergen-specific IgE antibodies, two different methods can be used: a skin prick test, or an allergy. Both methods are recommended, and they have similar diagnostic value.

Skin prick tests and blood tests are equally cost-effective, and health economic evidence shows that both tests were cost-effective compared with no test. Also, early and more accurate diagnoses save cost due to reduced consultations, referrals to secondary care, misdiagnosis, and emergency admissions.

Allergy undergoes dynamic changes over time. Regular allergy testing of relevant allergens provides information on if and how patient management can be changed, in order to improve health and quality of life. Annual testing is often the practice for determining whether allergy to milk, egg, soy, and wheat have been outgrown, and the testing interval is extended to 2–3 years for allergy to peanut, tree nuts, fish, and crustacean shellfish. Results of follow-up testing can guide decision-making regarding whether and when it is safe to introduce or re-introduce allergenic food into the diet.

Skin prick testing
Skin testing is also known as "puncture testing" and "prick testing" due to the series of tiny punctures or pricks made into the patient's skin. Small amounts of suspected allergens and/or their (e.g., pollen, grass, mite proteins, peanut extract) are introduced to sites on the skin marked with pen or dye (the ink/dye should be carefully selected, lest it cause an allergic response itself). A small plastic or metal device is used to puncture or prick the skin. Sometimes, the allergens are injected "intradermally" into the patient's skin, with a needle and syringe. Common areas for testing include the inside forearm and the back.

If the patient is allergic to the substance, then a visible inflammatory reaction will usually occur within 30 minutes. This response will range from slight reddening of the skin to a full-blown (called "wheal and flare") in more sensitive patients similar to a. Interpretation of the results of the skin prick test is normally done by allergists on a scale of severity, with +/− meaning borderline reactivity, and 4+ being a large reaction. Increasingly, allergists are measuring and recording the diameter of the wheal and flare reaction. Interpretation by well-trained allergists is often guided by relevant literature. Some patients may believe they have determined their own allergic sensitivity from observation, but a skin test has been shown to be much better than patient observation to detect allergy.

If a serious life-threatening anaphylactic reaction has brought a patient in for evaluation, some allergists will prefer an initial blood test prior to performing the skin prick test. Skin tests may not be an option if the patient has widespread skin disease, or has taken in the last several days.

Patch testing
Patch testing is a method used to determine if a specific substance causes allergic inflammation of the skin. It tests for delayed reactions. It is used to help ascertain the cause of skin contact allergy, or. Adhesive patches, usually treated with a number of common allergic chemicals or skin sensitizers, are applied to the back. The skin is then examined for possible local reactions at least twice, usually at 48 hours after application of the patch, and again two or three days later.

Blood testing
An allergy is quick and simple, and can be ordered by a licensed health care provider (e.g., an allergy specialist) or general practitioner. Unlike skin-prick testing, a blood test can be performed irrespective of age, skin condition, medication, symptom, disease activity, and pregnancy. Adults and children of any age can get an allergy blood test. For babies and very young children, a single needle stick for allergy blood testing is often more gentle than several skin pricks.

An allergy blood test is available through most. A sample of the patient's blood is sent to a laboratory for analysis, and the results are sent back a few days later. Multiple allergens can be detected with a single blood sample. Allergy blood tests are very safe, since the person is not exposed to any allergens during the testing procedure.

The test measures the concentration of specific in the blood. IgE test results increase the possibility of ranking how different substances may affect symptoms. A rule of thumb is that the higher the IgE antibody value, the greater the likelihood of symptoms. Allergens found at low levels that today do not result in symptoms can not help predict future symptom development. The quantitative allergy blood result can help determine what a patient is allergic to, help predict and follow the disease development, estimate the risk of a severe reaction, and explain.

A low total IgE level is not adequate to rule out to commonly inhaled allergens. , such as s, predictive value calculations, and likelihood ratios have been used to examine the relationship of various testing methods to each other. These methods have shown that patients with a high total IgE have a high probability of allergic sensitization, but further investigation with allergy tests for specific IgE antibodies for a carefully chosen of allergens is often warranted.

Laboratory methods to measure specific IgE antibodies for allergy testing include (ELISA, or EIA),  (RAST) and fluorescent enzyme  (FEIA).

Other testing
Challenge testing: Challenge testing is when small amounts of a suspected allergen are introduced to the body orally, through inhalation, or via other routes. Except for testing food and medication allergies, challenges are rarely performed. When this type of testing is chosen, it must be closely supervised by an.

Elimination/challenge tests: This testing method is used most often with foods or medicines. A patient with a suspected allergen is instructed to modify his diet to totally avoid that allergen for a set time. If the patient experiences significant improvement, he may then be "challenged" by reintroducing the allergen, to see if symptoms are reproduced.

Unreliable tests: There are other types of allergy testing methods that are unreliable, including (allergy testing through muscle relaxation),  testing, urine autoinjection, skin  (Rinkel method), and provocative and neutralization (subcutaneous) testing or sublingual provocation.

Differential diagnosis
Before a diagnosis of allergic disease can be confirmed, other possible causes of the presenting symptoms should be considered. , for example, is one of many illnesses that share symptoms with allergic rhinitis, underscoring the need for professional differential diagnosis. Once a diagnosis of, rhinitis, , or other allergic disease has been made, there are several methods for discovering the causative agent of that allergy.

Prevention
Giving peanut products early may decrease the risk allergies while only during at least the first few months of life may decrease the risk of. There is no good evidence that a mother's diet during or breastfeeding affects the risk. Nor is there evidence that delayed introduction of certain foods is useful. Early exposure to potential allergens may actually be protective.

Fish oil supplementation during pregnancy is associated with a lower risk. Probiotic supplements during pregnancy or infancy may help to prevent.

Management
Management of allergies typically involves avoiding what triggers the allergy and medications to improve the symptoms. may be useful for some types of allergies.

Medication
Several medications may be used to block the action of allergic mediators, or to prevent activation of cells and processes. These include s, s, (adrenaline), s, and s are common treatments of allergic diseases. , s, and other compounds thought to impair, are also commonly used. Although rare, the severity of often requires  injection, and where medical care is unavailable, a device known as an  may be used.

Immunotherapy
Allergen is useful for environmental allergies, allergies to insect bites, and asthma. Its benefit for food allergies is unclear and thus not recommended. Immunotherapy involves exposing people to larger and larger amounts of allergen in an effort to change the immune system's response.

Meta-analyses have found that injections of allergens under the skin is effective in the treatment in allergic rhinitis in children and in asthma. The benefits may last for years after treatment is stopped. It is generally safe and effective for allergic rhinitis and, allergic forms of asthma, and stinging insects.

The evidence also supports the use of for rhinitis and asthma but it is less strong. For seasonal allergies the benefit is small. In this form the allergen is given under the tongue and people often prefer it to injections. Immunotherapy is not recommended as a stand-alone treatment for asthma.

Alternative medicine
An experimental treatment, (EPD), has been tried for decades but is not generally accepted as effective. EPD uses dilutions of allergen and an enzyme,, to which are supposed to respond by favoring desensitization, or down-regulation, rather than sensitization. EPD has also been tried for the treatment of but evidence does not show effectiveness.

A review found no effectiveness of s and no difference compared with. The authors concluded that, based on rigorous clinical trials of all types of homeopathy for childhood and adolescence ailments, there is no convincing evidence that supports the use of homeopathic treatments.

According to the, U.S, the evidence is relatively strong that and  are effective, when compared to other  treatments, for which the scientific evidence is weak, negative, or nonexistent, such as honey, acupuncture, omega 3's, probiotics, astragalus, capsaicin, grape seed extract, Pycnogenol, quercetin, spirulina, stinging nettle, tinospora or guduchi.

Epidemiology
The allergic diseases—hay fever and asthma—have increased in the over the past 2–3 decades. Increases in allergic asthma and other atopic disorders in industrialized nations, it is estimated, began in the 1960s and 1970s, with further increases occurring during the 1980s and 1990s, although some suggest that a steady rise in sensitization has been occurring since the 1920s. The number of new cases per year of atopy in developing countries has, in general, remained much lower.

Changing frequency
Although genetic factors govern susceptibility to atopic disease, increases in 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 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 1 type responses, leading to unrestrained TH2 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. Evidence has shown that exposure to food and pathogens, such as, ', and ' (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 TH1/TH2 regulation. Important elements of newer hygiene hypotheses also include exposure to s, exposure to s and growing up on a farm.

History
Some signs and symptoms attributable to allergic diseases are mentioned in ancient sources. Particularly, three members of the Roman (,  and ) are suspected to have a family history of. The concept of "allergy" was originally introduced in 1906 by the , after he noticed that patients who had received injections of horse serum or smallpox vaccine usually had quicker, more severe reactions to second injections. Pirquet called this phenomenon "allergy" from the words  allos meaning "other" and  ergon meaning "work".

All forms of hypersensitivity used to be classified as allergies, and all were thought to be caused by an improper activation of the immune system. Later, it became clear that several different mechanisms were implicated, with the common link to a disordered activation of the immune system. In 1963, a new classification scheme was designed by and  that described four types of, known as Type I to Type IV hypersensitivity. With this new classification, the word allergy, sometimes clarified as a true allergy, was restricted to type I hypersensitivities (also called immediate hypersensitivity), which are characterized as rapidly developing reactions involving IgE antibodies.

A major breakthrough in understanding the mechanisms of allergy was the discovery of the antibody class labeled (IgE). IgE was simultaneously discovered in 1966–67 by two independent groups: 's team at the Children's Asthma Research Institute and Hospital in Denver, Colorado, and by Gunnar Johansson and Hans Bennich in Uppsala, Sweden. Their joint paper was published in April 1969.

Diagnosis
Radiometric assays include the (RAST test) method, which uses IgE-binding (anti-IgE) antibodies labeled with s for quantifying the levels of IgE antibody in the blood. Other newer methods use colorimetric or fluorescence-labeled technology in the place of radioactive isotopes.

The RAST methodology was invented and marketed in 1974 by Pharmacia Diagnostics AB, Uppsala, Sweden, and the acronym RAST is actually a brand name. In 1989, Pharmacia Diagnostics AB replaced it with a superior test named the ImmunoCAP Specific IgE blood test, which uses the newer fluorescence-labeled technology.

(ACAAI) and the (AAAAI) issued the Joint Task Force Report "Pearls and pitfalls of allergy diagnostic testing" in 2008, and is firm in its statement that the term RAST is now obsolete:

"The term RAST became a colloquialism for all varieties of (in vitro allergy) tests. This is unfortunate because it is well recognized that there are well-performing tests and some that do not perform so well, yet they are all called RASTs, making it difficult to distinguish which is which. For these reasons, it is now recommended that use of RAST as a generic descriptor of these tests be abandoned."

The new version, the ImmunoCAP Specific IgE blood test, is the only specific IgE assay to receive approval to quantitatively report to its detection limit of 0.1kU/l.

Medical specialty
An allergist is a physician specially trained to manage and treat allergies, and the other allergic diseases. In the United States physicians holding certification by the (ABAI) have successfully completed an accredited educational program and evaluation process, including a proctored examination to demonstrate knowledge, skills, and experience in patient care in allergy and immunology. Becoming an allergist/immunologist requires completion of at least nine years of training. After completing medical school and graduating with a medical degree, a physician will undergo three years of training in (to become an internist) or  (to become a pediatrician). Once physicians have finished training in one of these specialties, they must pass the exam of either the (ABP), the  (AOBP), the  (ABIM), or the  (AOBIM). Internists or pediatricians wishing to focus on the sub-specialty of allergy-immunology then complete at least an additional two years of study, called a fellowship, in an allergy/immunology training program. Allergist/immunologists listed as ABAI-certified have successfully passed the certifying examination of the ABAI following their fellowship.

In the United Kingdom, allergy is a subspecialty of or. After obtaining postgraduate exams ( or ), a doctor works for several years as a before qualifying for the  specialist register. Allergy services may also be delivered by s. A 2003 report presented a case for improvement of what were felt to be inadequate allergy services in the UK. In 2006, the convened a subcommittee. It concluded likewise in 2007 that allergy services were insufficient to deal with what the Lords referred to as an "allergy epidemic" and its social cost; it made several recommendations.

Research
Low-allergen foods are being developed, as are improvements in skin prick test predictions; evaluation of the patch test; in wasp sting outcomes predictions and a rapidly disintegrating epinephrine tablet, and anti- for eosinophilic diseases.

is the study of the biological particles passively dispersed through the air. One aim is the prevention of allergies due to pollen.