[2] The underlying mechanism involves immunoglobulin E antibodies (IgE), part of the body's immune system, binding to an allergen and then to a receptor on mast cells or basophils where it triggers the release of inflammatory chemicals such as histamine.

[30] With insect stings, a large local reaction may occur in the form of an area of skin redness greater than 10 cm in size that can last one to two days.

When an allergen enters the epidermis or dermis, it triggers a localized allergic reaction which activates the mast cells in the skin resulting in an immediate increase in vascular permeability, leading to fluid leakage and swelling in the affected area.

The mite's gut contains potent digestive enzymes (notably peptidase 1) that persist in their feces and are major inducers of allergic reactions such as wheezing.

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.

[56][57] The resulting dermatological response to the reaction between urushiol and membrane proteins includes redness, swelling, papules, vesicles, blisters, and streaking.

In general, approximately 80–90% of adults will develop a rash if they are exposed to 0.0050 mg (7.7×10−5 gr) of purified urushiol, but some people are so sensitive that it takes only a molecular trace on the skin to initiate an allergic reaction.

[63] Ethnicity may play a role in some allergies; however, racial factors have been difficult to separate from environmental influences and changes due to migration.

[61] It has been suggested that different genetic loci are responsible for asthma, to be specific, in people of European, Hispanic, Asian, and African origins.

The identified genes associated with allergic disease severity, progression, and development primarily function in four areas: regulating inflammatory responses (IFN-α, TLR-1, IL-13, IL-4, IL-5, HLA-G, iNOS), maintaining vascular endothelium and mucosal lining (FLG, PLAUR, CTNNA3, PDCH1, COL29A1), mediating immune cell function (PHF11, H1R, HDC, TSLP, STAT6, RERE, PPP2R3C), and influencing susceptibility to allergic sensitization (e.g., ORMDL3, CHI3L1).

[65] Multiple studies have investigated the genetic profiles of individuals with predispositions to and experiences of allergic diseases, revealing a complex polygenic architecture.

[65] These genes engage in shared inflammatory pathways across various epithelial tissues—such as the skin, esophagus, vagina, and lung—highlighting common genetic factors that contribute to the pathogenesis of asthma and other allergic diseases.

[71] 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.

[86] However, the research to support this theory is conflicting, with some studies performed in China and Ethiopia showing an increase in allergy in people infected with intestinal worms.

Activated mast cells and basophils undergo a process called degranulation, during which they release histamine and other inflammatory chemical mediators (cytokines, interleukins, leukotrienes, and prostaglandins) from their granules into the surrounding tissue causing several systemic effects, such as vasodilation, mucous secretion, nerve stimulation, and smooth muscle contraction.

[93][94] Correct diagnosis, counseling, and avoidance advice based on valid allergy test results reduce the incidence of symptoms and need for medications, and improve quality of life.

[93] Early and more accurate diagnoses save cost due to reduced consultations, referrals to secondary care, misdiagnosis, and emergency admissions.

Regular allergy testing of relevant allergens provides information on if and how patient management can be changed to improve health and quality of life.

This response will range from slight reddening of the skin to a full-blown hive (called "wheal and flare") in more sensitive patients similar to a mosquito bite.

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.

For babies and very young children, a single needle stick for allergy blood testing is often gentler than several skin pricks.

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 cross-reactivity.

[111] Once a diagnosis of asthma, rhinitis, anaphylaxis, or other allergic disease has been made, there are several methods for discovering the causative agent of that allergy.

These include antihistamines, glucocorticoids, epinephrine (adrenaline), mast cell stabilizers, and antileukotriene agents are common treatments of allergic diseases.

[124] EPD uses dilutions of allergen and an enzyme, beta-glucuronidase, to which T-regulatory lymphocytes are supposed to respond by favoring desensitization, or down-regulation, rather than sensitization.

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.

[125] According to the National Center for Complementary and Integrative Health, U.S., the evidence is relatively strong that saline nasal irrigation and butterbur are effective, when compared to other alternative medicine 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.

[85][144] 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.

IgE was simultaneously discovered in 1966–67 by two independent groups:[154] Ishizaka's team at the Children's Asthma Research Institute and Hospital in Denver, USA,[155] and by Gunnar Johansson and Hans Bennich in Uppsala, Sweden.

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.