Allergic reactions: types, symptoms and help

An allergic reaction is an excessive immune response to an external or internal antigen, which is harmless in most people. Symptoms vary widely, from a runny nose and itchy skin to anaphylaxis, which is considered an emergency. Several immunological mechanisms of hypersensitivity are now recognized, so "allergy" is not a single disease, but a whole spectrum of conditions with different biology and different treatment approaches. [1]

Over the past decades, the prevalence of allergic diseases has increased in many countries. This is influenced by genetic predisposition and environmental factors, including air pollution, climate change, urbanization, and microbial exposure patterns in early childhood. This multifactorial nature means there are no universal "magic pills": effective care relies on an accurate diagnosis, risk stratification, and a personalized treatment plan. [2]

Clinical scenarios vary in speed of onset and severity. Immediate reactions, mediated by immunoglobulin E, develop within minutes and can lead to urticaria, bronchospasm, and anaphylaxis. Delayed reactions, mediated by T cells, develop over hours or days and more often present with dermatitis. Understanding the mechanism determines the choice of tests and therapy, so accurate classification is not an academic formality but a practical necessity. [3]

Healthcare systems are updating their approaches to recording allergic conditions. The latest edition of the International Classification of Diseases (ICD) has expanded the "Allergic and Hypersensitivity Conditions" section, which helps identify the true burden of diseases and compare data across countries. This directly benefits patients: accurate coding improves routing, access to treatment, and quality of care statistics. [4]

Code according to the International Classification of Diseases, 10th and 11th revisions

In the International Classification of Diseases, Tenth Revision, allergic reactions are classified into several chapters. Anaphylaxis and some "unspecified" allergic conditions are coded in block T78, urticaria in group L50, allergic rhinitis in group J30, and bronchial asthma in group J45. This reflects clinical diversity and requires careful code selection for a specific situation. [5]

The International Classification of Diseases, Eleventh Revision, has made significant progress: it has created a unified architecture for "Allergic and Hypersensitivity Disorders," detailed the types of anaphylaxis and induced urticaria, and clarified the entries for allergic rhinitis and asthma phenotypes. For example, "allergic asthma" has a separate category, and anaphylaxis is differentiated by cause, which is important for epidemiology and reimbursement. [6]

Table 1. Examples of correspondence between frequently used ICD-10 ↔ ICD-11 codes

State	ICD-10 (example)	ICD-11 (example)
Anaphylaxis, unspecified	T78.2	4A84.Z
Anaphylaxis due to food	T78.0	4A84.0
Allergic rhinitis	J30.*	CA08.0 and subsidiaries
Hives	L50.*	EB00-EB01 and subsidiaries
Allergic asthma	J45.0	CA23.0
Contact allergic dermatitis	L23.*	EK00.*

Epidemiology

Allergic rhinitis remains one of the most common allergic conditions worldwide. Estimates of prevalence in populations vary widely, from 10% to 30% or more, depending on the research methodology and region. In recent years, the contribution of climate and urbanization, which lengthen pollen seasons and increase exposure to pollutants, has been discussed. [7]

Food allergy is a significant cause of emergency room visits, particularly in children. Large surveys have found prevalence in children to be between 6-8% and up to 10%, although clinically confirmed figures are lower than self-reported prevalence. Recent national projects indicate that clinically confirmed allergy occurs in approximately 6% of adults in several countries, highlighting the importance of accurate diagnosis. [8]

Atopic dermatitis and bronchial asthma constitute a significant global disease burden. Global studies estimate that in 2021, approximately 260 million people suffered from asthma and approximately 129 million from atopic dermatitis. These data are important for healthcare planning and explain the interest in biologics that target key inflammatory pathways. [9]

Urticaria (especially the chronic spontaneous form) is common throughout life, while induced forms (cold, dermatographic, solar) are less common but significantly impair quality of life. Global estimates indicate tens of millions of cases, with a higher incidence in women and young people. [10]

Table 2. Estimates of the prevalence of key allergic conditions

State	Approximate prevalence estimates	Sources
Allergic rhinitis	10-30% of the population	[11]
Food allergy	Up to 8% in children, up to 10% in adults; lower if confirmed by tests	[12]
Bronchial asthma	About 260 million people in 2021	[13]
Atopic dermatitis	About 129 million people in 2021	[14]
Hives (in general)	Tens of millions of cases worldwide	[15]

Reasons

Allergic sensitization occurs when the immune system encounters allergens and subsequently produces immunoglobulin E antibodies, which bind to mast cells and basophils. Repeated exposure triggers the release of inflammatory mediators and the development of symptoms. This mechanism underlies immediate reactions to food proteins, aeroallergens, and Hymenoptera venom. [16]

Delayed reactions develop differently: the key role is played by T cells, which recognize the antigen after its processing in the skin. This mechanism is characteristic of allergic contact dermatitis and a number of drug hypersensitivities. These forms typically develop within 24-72 hours and require a different diagnostic approach. [17]

It's not just the immune system that sets the stage. Environmental factors also play a significant role: air pollution increases respiratory inflammation and increases the risk of sensitization, while climate change lengthens pollen seasons and increases allergen concentrations in the air. This explains the increase in symptoms among city dwellers and those in regions with severe environmental conditions. [18]

Finally, early childhood "microbial experiences" contribute. A modern interpretation of the classical "hygiene hypothesis" suggests that varied and timely microbial exposure helps the immune system properly develop tolerance, reducing the risk of allergic diseases. [19]

Table 3. Biological mechanisms of allergy in large smears

Mechanism	Cells and molecules	A typical clinic
Immediate response to immunoglobulin E	Mast cells, basophils, histamine, leukotrienes	Urticaria, rhinitis, asthma, anaphylaxis
Immune complexes	Antibodies and antigens in the blood, complement	Serum sickness and similar reactions
Cytotoxic reactions	Antibodies against one's own cells	Hematological drug reactions
delayed-type T-cell response	Sensitized T lymphocytes	Contact dermatitis, part of drug reactions

Risk factors

A family history increases the likelihood of developing allergies: if one parent has an allergic disease, the child's risk is higher, and if both parents have it, the risk is even higher. This isn't a "sentence," but an important marker that can be used to guide early prevention and monitoring. [20]

Urban environments and air pollution exacerbate rhinitis and asthma symptoms and are associated with increased sensitization. Observational and experimental studies agree: particles and gases damage the epithelium, facilitating the penetration of allergens, and also alter the behavior of pollen. [21]

Climate change is lengthening seasons and increasing pollen allergenicity; extreme weather events, including "thunderstorm asthma," are associated with surges in hospital visits. These effects are particularly pronounced in people with pre-existing respiratory conditions. [22]

Early microbial environment, nutrition, and contact with animals can influence risk through the development of immune tolerance. Recent reviews clarify that this isn't about "dirt," but rather about the diversity of safe microbial stimuli that accompany a healthy lifestyle. [23]

Table 4. What increases the risk of allergies

Factor	How does it affect	Example of practical conclusion
Heredity	It sets the immune system's high readiness for sensitization	Close monitoring by a pediatrician and allergist
Air pollution	Damages the epithelium and increases inflammation	Exposure control, indoor air purification
Climate change	They prolong the pollen season and increase allergenicity.	Preventive therapy during the seasons, pollen monitoring
Lack of microbial diversity	Reduces tolerance formation	Balance of hygiene and natural contact with nature

Pathogenesis

In immediate allergic reactions, sensitization plays a key role, with the formation of immunoglobulin E antibodies. These antibodies bind to mast cells and basophils; repeated exposure to the allergen leads to cross-linking of receptors and the release of inflammatory mediators. The clinical outcome is itching, swelling, bronchospasm, and other symptoms within minutes. [24]

In a delayed-type reaction, the immune system uses a different "tool"—sensitized T cells. Upon repeated exposure, they trigger a cascade of cytokines, attracting macrophages and other cells, causing inflammation and tissue damage. This mechanism determines the clinical presentation of contact dermatitis and some drug hypersensitivities. [25]

Modern allergology is moving away from a crude approach toward phenotypes and endotypes—stable combinations of clinical features and biological pathways. This allows for the prediction of response to therapy, including targeted drugs, and explains why two patients with identical symptoms have different disease "biologies." [26]

An important example is asthma: different inflammatory axes may predominate in different patients with the same diagnosis. Understanding these differences helps select inhaled and biologic drugs that target key mediators and interleukins. [27]

Symptoms

The skin and mucous membranes are common sites for allergic reactions. Urticaria and angioedema manifest as itchy blisters and swelling, allergic rhinitis as sneezing, nasal congestion, and watery discharge, and conjunctivitis as redness and watery eyes. These symptoms often worsen with contact with certain allergens and subside after their elimination. [28]

Food reactions range from local oral symptoms to systemic manifestations, including vomiting, diarrhea, bronchospasm, and a drop in blood pressure. In children, food reactions are the leading cause of anaphylaxis; in adults, the spectrum of causes is broader and includes drugs and hymenoptera venoms.[29]

Respiratory manifestations range from episodic wheezing to the typical picture of bronchial asthma with nocturnal symptoms and activity limitation. In many patients, allergic rhinitis and asthma coexist, which is explained by the concept of "single airway." This requires coordinated therapy of the upper and lower airways. [30]

Anaphylaxis is the most dangerous form of allergic reaction. It develops quickly, within minutes, and requires immediate intramuscular administration of adrenaline. After an episode, all patients are advised to consult a specialist to determine the cause and learn how to prevent recurrences. [31]

Classification, forms and stages

The classical Gell and Coombs system distinguishes four types of hypersensitivity based on mechanism: immediate immunoglobulin E reactions, cytotoxic reactions, immune complex reactions, and delayed-type T-cell reactions. Clinically, these often overlap, but this framework remains useful for selecting tests and identifying therapeutic targets. [32]

Modern approaches complement classification with phenotypes and endotypes reflecting specific molecular pathways. This has been particularly evident in asthma and atopic dermatitis, where the choice of biological therapy depends on the dominant cytokines and cell populations. This approach is gradually being extended to other allergic diseases. [33]

Clinical forms of allergy include rhinitis, conjunctivitis, asthma, atopic dermatitis, urticaria and angioedema, food allergies, drug hypersensitivity, and reactions to insect venoms. Each form has its own unique triggers, course, and risk of complications, so there are no "universal" diagnostic and treatment protocols. [34]

Staging is appropriate for some diseases. For example, chronic forms (allergic rhinitis, atopic dermatitis, asthma) go through phases of exacerbation and remission, requiring different treatment and prevention strategies. Keeping a diary of symptoms and factors allows us to record the dynamics and evaluate the effectiveness of interventions. [35]

Table 5. Classification scheme of allergic reactions

Level	Examples
Mechanisms of hypersensitivity	Immediate immunoglobulin E, cytotoxic, immune complex, cellular delayed type
Phenotypes	Allergic rhinitis, asthma, atopic dermatitis, urticaria, food and drug allergies
Endotypes	Prevalence of specific cytokine pathways and cells (for selection of targeted therapy)

Complications and consequences

Untreated allergic rhinitis increases the risk of asthma exacerbations and reduces productivity, sleep quality, and academic performance in children. In the real world, it is these "unnoticed" chronic symptoms that create the greatest overall loss of quality of life and economic costs. [36]

Food allergies carry the risk of anaphylaxis and psychological burden: anxiety in anticipation of a reaction, dietary restrictions, and social difficulties. A confirmed diagnosis and a clear action plan reduce the risk and improve quality of life, and new treatments complement the avoidance strategy. [37]

Chronic urticaria and angioedema cause significant discomfort, sleep disturbance, and a high rate of physician visits. Even in "benign" forms, treatment is important to control symptoms and reduce the risk of progression. [38]

Anaphylaxis is dangerous due to its recurrence and unpredictability. Each patient needs a personalized plan after an episode: training in symptom recognition, immediate administration of epinephrine, specialist monitoring, and assessment of the need for autoinjectors. [39]

When to see a doctor

If recurring symptoms occur regularly after exposure to specific foods, medications, pollen, or insect bites, this is a reason to visit an allergist. Self-monitoring is not enough: it is important to determine the mechanism of the reaction and confirm the clinical significance of sensitization. [40]

Emergency care is required if signs of anaphylaxis appear: rapidly increasing itching and redness, swelling of the lips or tongue, wheezing, difficulty inhaling and exhaling, a drop in blood pressure, or fainting. The first step is intramuscular adrenaline, followed by calling an ambulance and hospital observation. [41]

For chronic nasal, eye, skin, or respiratory symptoms, it's worth discussing an evaluation and treatment plan. The goal is not simply to "dull" symptoms, but to reduce the overall risk, including asthma flare-ups and skin infections due to scratching. [42]

If a child has a family history of allergies and early signs of sensitization, it is reasonable to discuss prevention and early therapy in a planned manner to reduce the disease burden and preserve the family's quality of life. [43]

Diagnostics

Step 1. A detailed allergy assessment and examination. The doctor clarifies when and under what circumstances the symptoms occur, how quickly they develop, how long they last, and what helps. Potential triggers, concomitant illnesses, and family history are recorded. This is the most important step: a thorough interview significantly narrows the range of probable causes. [44]

Step 2. Screening skin tests and blood tests for specific antibodies. Skin prick tests with commercial extracts or fresh products, under standardized methods, provide a rapid answer to the question of probable sensitization. Blood tests for specific IgE antibodies are useful when skin tests are impossible or unsafe, as well as for monitoring. Results are interpreted only in conjunction with the symptom history. [45]

Step 3. Molecular diagnostics and functional tests as indicated. Component-resolving diagnostics helps distinguish "true" primary sensitization from cross-sensitization and assess the risk of severe reactions. A basophil activation test provides functional confirmation of the clinical significance of sensitization in some patients when doubts remain. These tools reduce the need for risky provocations. [46]

Step 4. Provocative testing under conditions where it is justified and safe. Oral food and drug challenges are performed according to strict protocols in specialized centers when they are essential for answering key diagnostic questions. For drug allergies, there are position papers on the methodology and safety of such tests. [47]

Table 6. Diagnostic tools and their role

Method	What does it show?	Where it is especially useful
Skin prick tests	Presence of sensitization	Rhinitis, asthma, food allergies
Specific antibodies of the immunoglobulin E class	Blood sensitization	When skin testing is not possible
Component-resolving diagnostics	Risk and cross-reactions	Food and inhalation allergies
Basophil activation test	Functional reactivity	Complex cases, saving provocations
Provocative tests	Clinical significance	Food, medicines, according to strict indications

Differential diagnosis

It is important to distinguish allergic rhinitis from non-allergic rhinitis, infections, and drug-induced forms. "Red flags" include persistent unilateral congestion, bloody discharge, severe pain, and high fever. With a typical seasonal pattern and positive tests, the diagnosis is obvious; with an atypical course, further testing is required. [48]

Food allergies differ from intolerances where the immune system is not involved (for example, enzymatic lactose intolerance). When in doubt, molecular tests and provocations under observation are used. It is important not to make an unfounded diagnosis, to avoid unnecessary dietary restrictions. [49]

Skin manifestations must be distinguished from infections, autoimmune dermatoses, and toxicoderma. Drug reactions have a wide range of mechanisms, so decisions regarding skin testing and provocations are made by a specialized team, taking into account the risks. [50]

Anaphylaxis is differentiated from vasovagal reactions, panic attacks, and asthma exacerbations without systemic involvement. In doubtful cases, clinical diagnostic criteria and blood tryptase measurement in the immediate hours after the episode are helpful. [51]

Table 7. Common allergy masks and how to recognize them

Situation	"For" allergies	Against allergies
Runny nose	Seasonality, itching, sneezing, response to antihistamines	Pus, high temperature, one-sidedness
Rash	Clear connection with the allergen, itching, rapid dynamics	Pain, necrosis, blisters with systemic reaction
Respiratory symptoms	Combination with rhinitis, wheezing	Isolated shortness of breath on exertion without other symptoms
Gastrointestinal symptoms	Rapid reactions to certain foods	Persistent symptoms not related to food

Treatment

The basic principle for all forms of allergy is exposure management. This doesn't always mean "living in a sterile room," but rather thoughtful steps: reducing exposure to causative allergens, controlling house dust, air filtration, pollen monitoring, and being careful with food allergens. For insect venoms, this includes bite prevention and, if indicated, allergen-specific venom immunotherapy. These measures reduce the need for medications and increase their effectiveness. [52]

Pharmacotherapy is tailored to the phenotype and severity. For allergic rhinitis, intranasal corticosteroids have been proven to be first-line treatments, supplemented with oral or intranasal histamine H1 receptor blockers and isotonic saline rinses. For conjunctivitis, antihistamines or mast cell stabilizers in drops are helpful. The choice depends on the predominant symptoms and tolerability. [53]

Bronchial asthma requires step-by-step therapy with inhaled corticosteroids as the basis. Current strategies emphasize the controlled use of inhaled corticosteroids in combination with bronchodilators on an as-needed or daily basis to reduce exacerbations. In severe cases, biologic agents targeting key inflammatory pathways are considered. [54]

Allergen-specific immunotherapy is the only method that modifies the natural history of allergy to inhalant allergens. Courses of sublingual or subcutaneous immunotherapy reduce rhinitis and asthma symptoms, reduce the need for medications, and maintain the effect after therapy is completed. Indications, allergen composition, and safety are determined by guidelines and the individual patient profile. [55]

In food allergies, avoidance of offending foods and preparedness for immediate action remain the cornerstone. A new development is the ability to use omalizumab to reduce the risk of reactions to accidental exposure to multiple food allergens in people with immunoglobulin E-mediated allergies. This does not replace avoidance, but may improve the safety of daily living in carefully selected patients. [56]

Anaphylaxis is an emergency, and the first and primary treatment is intramuscular adrenaline in the anterolateral thigh. The dose for healthcare workers is calculated based on body weight at a rate of 0.01 milligrams per kilogram, with a maximum of 0.5 milligrams in adults. If life-threatening symptoms persist, the dose is repeated after 5 minutes. Intravenous administration is prohibited outside of specialized settings. [57]

Chronic urticaria often requires long-term courses of non-sedating histamine H1 receptor blockers, with doses increased to the recommended doses in specialized documents if the response is insufficient. Omalizumab is effective in refractory cases; alternative immunomodulators are being considered in specialized centers in some cases. [58]

In patients with severe asthma and chronic rhinosinusitis with polyps, indications for biological therapy are expanding. Drugs targeting interleukins and key inflammatory "gateway" molecules improve symptom control, reduce the need for systemic steroids, and reduce the frequency of exacerbations. New regulatory approvals for the treatment of chronic rhinosinusitis with polyps will be available in 2025, expanding options for patients. [59]

Drug hypersensitivity requires a special strategy. The key is precise verification of the mechanism and the culprit drug, so as not to "prohibit" unnecessary substances whenever possible. Standardized skin tests, laboratory methods, and carefully planned provocations help safely narrow the list of restrictions and select alternatives. Where possible, desensitization is carried out under the supervision of a specialized team. [60]

Table 8. Therapy roadmap by clinical phenotypes

Phenotype	Base	Escalation	Comments
Allergic rhinitis	Intranasal corticosteroids, histamine H1 receptor blockers	Allergen-specific immunotherapy	Selection based on seasonality and sensitization profile
Asthma	Inhaled corticosteroids according to the 2025 strategy	Biological drugs for severe cases	A unified approach to the upper and lower paths
Food allergy	Avoidance, education, autoinjector at risk	Omalizumab in selected patients	Avoidance remains mandatory
Hives	Non-sedating histamine H1 receptor blockers	Omalizumab, other indications	Stepped scheme
Drug hypersensitivity	Exclusion of the causative drug	Desensitization for strict indications	Only in specialized centers

Prevention

Prevention begins with knowing your triggers. For inhaled allergens, pollen monitoring apps and services, high-efficiency air filters, and bedroom hygiene are helpful. For food allergies, it's important to read labels carefully, prevent cross-contamination, and educate loved ones on allergy first aid. [61]

Vaccinations and chronic disease management reduce nonspecific exacerbations. Preventing upper respiratory infections, smoking cessation, and weight control reduce inflammation and increase the effectiveness of basic allergy therapy. These are simple steps with a big impact. [62]

Environmental measures are particularly relevant in cities: reducing exposure to pollutants, proper ventilation, and using air purifiers with sufficient air exchange rates. Vulnerable groups—children and the elderly—benefit most from such interventions. [63]

Training is key. Patients at risk for anaphylaxis should be trained to recognize the early signs and administer epinephrine promptly. After any serious episode, a routine consultation with a specialist is required to clarify the diagnosis, review prevention plans, and refresh skills. [64]

Table 9. Preventive measures and expected benefits

Measure	Who is it especially useful for?	Expected effect
Exposure control and pollen monitoring	Allergic rhinitis, asthma	Fewer flare-ups and fewer medication needs
Anaphylaxis Education and Action Plan	Food and drug allergies, reactions to insect venoms	Reduction in mortality and hospitalizations
Indoor air purification	City dwellers, children, elderly	Improvement of symptoms and sleep
Allergen-specific immunotherapy	Rhinitis and asthma with proven sensitization	Long-term reduction of symptoms

Forecast

Most people with allergic rhinitis and mild asthma have a good prognosis with proper treatment and control of triggers. Consistency is key: regular therapy and correct use of inhalers reduce flare-ups and maintain lung function. [65]

Food allergies resolve over time in some children, but nut and fish allergies often persist for life. New approaches, including biologics and carefully controlled immunotherapy, are expanding options and improving quality of life. [66]

Chronic urticaria can persist for months or years, but most patients achieve control with a step-down regimen. The addition of targeted therapy in refractory cases significantly improves outcomes. [67]

The main factors contributing to poor outcomes are underrecognized asthma, underestimation of the risk of anaphylaxis, and non-adherence to the treatment plan. The solution is proper diagnosis, education, and up-to-date risk stratification, including an emergency action plan. [68]

FAQ

Are allergies and intolerances the same thing?
No. Allergies involve the immune system, while intolerances do not. Examples of intolerances include lactase deficiency and pharmacological reactions to certain food amino acids. Diagnostic approaches vary. [69]

Is it possible to "cure allergies permanently"?
In some cases, yes, by modifying the natural course of the disease with allergen-specific immunotherapy. In others, long-term symptom control and rare exacerbations are possible with basic therapy and exposure management. [70]

What's new in food allergy treatment?
Omalizumab has been shown to reduce the risk of reactions to multiple foods in patients with immunoglobulin E-mediated allergy. This complements, rather than replaces, strict avoidance measures and education. [71]

What is the first aid for suspected anaphylaxis?
Immediate intramuscular administration of adrenaline, calling an ambulance, and observation. If the threat persists, repeat the dose after 5 minutes. Intravenous administration should only be done in a specialized environment and by trained personnel. [72]

Why are molecular tests and basophil activation tests needed?
They help clarify the actual risk, distinguish cross-reactivity from primary sensitization, and avoid unnecessary provocations. They are used when basic tests and history do not provide a definitive answer. [73]