Allergic Rhinitis: Causes, Pathophysiology, Diagnosis, and Management

Introduction

Allergic rhinitis (AR) is one of the most prevalent chronic respiratory disorders worldwide, affecting hundreds of millions of individuals. It is characterized by inflammation of the nasal mucosa resulting from immunoglobulin E (IgE)–mediated hypersensitivity reactions to environmental allergens. Common symptoms include sneezing, nasal congestion, rhinorrhea, and nasal itching. Allergic rhinitis is not a life-threatening condition, but it has a significant impact on quality of life, productivity, and school performance.

Globally, the prevalence of allergic rhinitis has been steadily increasing due to rising environmental pollution, lifestyle changes, urbanization, and genetic predisposition. It can occur at any age but is most commonly diagnosed in childhood and early adulthood. The condition often coexists with other allergic diseases such as asthma, atopic dermatitis, and conjunctivitis, forming part of the “atopic march.”

This article explores the definition, types, causes, pathophysiology, clinical features, diagnostic methods, treatment options, and preventive measures for allergic rhinitis.

Definition

Allergic rhinitis is defined as an IgE-mediated inflammatory disorder of the nasal mucosa induced by exposure to allergens. The inflammation leads to nasal hyperresponsiveness, resulting in recurrent symptoms such as sneezing, nasal obstruction, itching, and watery discharge.

According to the Allergic Rhinitis and its Impact on Asthma (ARIA) guidelines, allergic rhinitis is classified based on duration and severity:

Intermittent Allergic Rhinitis: Symptoms occur less than four days per week or for less than four consecutive weeks.
Persistent Allergic Rhinitis: Symptoms occur more than four days per week and for more than four consecutive weeks.
Mild: Symptoms do not interfere with sleep, daily activities, or work.
Moderate to Severe: Symptoms interfere with normal functioning and sleep, leading to impairment in quality of life.

Epidemiology

Allergic rhinitis is a global health problem with increasing incidence across all age groups. Its prevalence varies geographically, influenced by climate, environmental exposure, and genetic factors. Studies estimate that up to 30% of adults and 40% of children suffer from allergic rhinitis worldwide.

In industrialized nations, allergic rhinitis has become one of the most common chronic diseases. Urban populations tend to have higher rates due to exposure to air pollutants, indoor allergens, and reduced microbial diversity, which can alter immune tolerance.

In developing countries, including those in South Asia and Africa, awareness and diagnosis rates are lower, but prevalence is gradually rising with increasing industrialization. The burden of disease is often underestimated, and many patients remain undiagnosed or inadequately treated.

Etiology (Causes)

Allergic rhinitis develops due to a complex interaction of genetic and environmental factors. The primary cause is sensitization of the immune system to allergens—substances that are typically harmless to most individuals but cause an allergic response in predisposed persons.

1. Genetic Factors

Family history of atopy (asthma, eczema, allergic rhinitis) increases the risk significantly.
Specific genes related to immune regulation, such as those encoding for IL-4, IL-13, and FcεRI receptors, play key roles.
Twin studies show a strong genetic predisposition, with heritability estimates between 50% and 70%.

2. Environmental Factors

Early life exposure to allergens, air pollution, and tobacco smoke.
Westernized lifestyle with decreased exposure to microbial agents (“hygiene hypothesis”).
Urban living and indoor environments with limited ventilation.
Seasonal changes and climate influence allergen levels (e.g., pollen, mold).

3. Common Allergens

Allergens are divided into indoor and outdoor categories:

Indoor Allergens:

House dust mites (Dermatophagoides pteronyssinus, D. farinae)
Pet dander (cats, dogs)
Cockroach droppings
Mold spores

Outdoor Allergens:

Pollen from grasses, trees (birch, oak), and weeds (ragweed)
Fungal spores
Environmental pollutants that act as adjuvants (diesel exhaust, ozone)

Pathophysiology

Allergic rhinitis results from a Type I hypersensitivity reaction mediated by IgE antibodies. The pathophysiology can be divided into two main phases:

1. Sensitization Phase

During initial exposure to an allergen:

The allergen is captured by antigen-presenting cells (APCs), such as dendritic cells, in the nasal mucosa.
These cells process and present the allergen to T-helper type 2 (Th2) lymphocytes.
Th2 cells release cytokines (IL-4, IL-5, IL-13) that promote B-cell differentiation into plasma cells.
Plasma cells produce allergen-specific IgE antibodies, which bind to receptors on mast cells and basophils.

This sensitization prepares the immune system for a heightened response upon re-exposure.

2. Re-Exposure Phase

When the individual encounters the same allergen again:

The allergen cross-links IgE molecules on mast cells, leading to mast cell degranulation.
This releases histamine, leukotrienes, prostaglandins, and cytokines.
These mediators cause vasodilation, increased vascular permeability, and mucus secretion, resulting in symptoms like sneezing, itching, and rhinorrhea.

3. Early and Late Phase Reactions

Early Phase (within minutes): Characterized by sneezing, itching, and watery discharge due to histamine release.
Late Phase (after 4–6 hours): Involves infiltration of eosinophils, basophils, and T-cells, leading to nasal congestion and chronic inflammation.

Chronic inflammation may result in nasal hyperresponsiveness to non-specific irritants such as smoke, perfume, and cold air.

Clinical Manifestations

The hallmark symptoms of allergic rhinitis are:

1. Nasal Symptoms

Sneezing: Often in paroxysms, particularly in the morning.
Rhinorrhea: Watery nasal discharge.
Nasal congestion: Due to mucosal swelling.
Nasal itching: Prominent and often associated with rubbing or wrinkling of the nose (“allergic salute”).

2. Ocular Symptoms (Allergic Conjunctivitis)

Itching, redness, and tearing of the eyes.
Periorbital darkening (“allergic shiners”).
Puffiness or swelling around the eyes.

3. Other Symptoms

Postnasal drip leading to throat clearing or cough.
Headache and facial pressure due to sinus obstruction.
Fatigue, irritability, and sleep disturbances due to chronic nasal blockage.

Complications

Untreated or poorly managed allergic rhinitis can lead to several complications:

Sinusitis: Chronic inflammation may obstruct sinus drainage, causing sinus infections.
Otitis Media: Eustachian tube dysfunction may result in middle ear effusion.
Asthma: AR and asthma often coexist; nasal inflammation can exacerbate lower airway symptoms.
Nasal Polyps: Chronic inflammation may cause benign growths in nasal passages.
Sleep Apnea: Persistent nasal obstruction can contribute to snoring and sleep apnea.

Diagnosis

Diagnosis of allergic rhinitis is based on clinical history, physical examination, and allergy testing.

1. Clinical History

Onset, duration, and pattern of symptoms.
Seasonal vs. perennial occurrence.
Family history of atopy.
Exposure to potential allergens (pets, dust, pollen).

2. Physical Examination

Typical findings include:

Pale, bluish, and swollen nasal mucosa.
Clear watery nasal discharge.
“Allergic salute” and nasal crease.
Mouth breathing or dark circles under eyes.

3. Diagnostic Tests

a) Skin Prick Test (SPT):

A small amount of allergen extract is applied to the skin.
A positive test shows a wheal-and-flare reaction within 15–20 minutes.
Highly sensitive and cost-effective.

b) Serum Specific IgE Test (RAST or ELISA):

Measures allergen-specific IgE antibodies in blood.
Useful when skin testing is contraindicated.

c) Nasal Cytology:

Eosinophilia in nasal secretions suggests allergic etiology.

d) Other Tests:

Imaging (CT/MRI) if chronic sinusitis is suspected.
Peak nasal inspiratory flow (PNIF) for assessing obstruction.

Differential Diagnosis

Conditions that may mimic allergic rhinitis include:

Nonallergic rhinitis: Triggered by irritants, temperature changes, or hormones.
Viral rhinitis (common cold): Usually self-limiting with fever and malaise.
Vasomotor rhinitis: Nonallergic and noninfectious cause of nasal hyperreactivity.
Rhinosinusitis: Associated with purulent discharge and facial pain.
Nasal polyposis or structural abnormalities.

Management

The management of allergic rhinitis involves environmental control, pharmacotherapy, and immunotherapy. The primary goal is to control symptoms, improve quality of life, and prevent complications.

1. Allergen Avoidance

Avoidance of allergens is the first-line approach and may significantly reduce symptom severity.

a) Dust Mite Control:

Use dust-proof covers on mattresses and pillows.
Wash bedding weekly in hot water (>55°C).
Remove carpets, heavy curtains, and stuffed toys from bedrooms.

b) Pet Dander Control:

Keep pets out of bedrooms or living areas.
Regular grooming and cleaning.

c) Pollen Avoidance:

Keep windows closed during high pollen seasons.
Use air conditioning and high-efficiency particulate air (HEPA) filters.
Shower and change clothes after outdoor activities.

d) Mold Control:

Reduce indoor humidity (<50%).
Fix water leaks and clean moldy areas.

2. Pharmacotherapy

Drug therapy is the mainstay of treatment for most patients and targets the inflammatory response.

a) Antihistamines

Block histamine receptors, reducing itching, sneezing, and rhinorrhea.
First-generation (e.g., diphenhydramine): Effective but sedating.
Second-generation (e.g., loratadine, cetirizine, fexofenadine): Non-sedating, preferred for daytime use.

b) Intranasal Corticosteroids

Most effective for controlling nasal inflammation and congestion.
Examples: fluticasone, mometasone, budesonide.
Long-term use is generally safe with minimal systemic absorption.

c) Decongestants

Relieve nasal blockage by vasoconstriction (pseudoephedrine, oxymetazoline).
Should be used for short periods (≤5 days) to avoid rebound congestion.

d) Leukotriene Receptor Antagonists

Block leukotriene-mediated inflammation.
Example: montelukast.
Useful in patients with both allergic rhinitis and asthma.

e) Mast Cell Stabilizers

Prevent mast cell degranulation.
Example: cromolyn sodium (effective prophylactically but less potent).

f) Combination Therapy

Intranasal corticosteroid + antihistamine (e.g., azelastine/fluticasone) provides superior relief.

3. Immunotherapy

Allergen-specific immunotherapy (ASIT) is the only disease-modifying treatment for allergic rhinitis. It involves controlled exposure to increasing doses of the allergen to induce immune tolerance.

a) Routes:

Subcutaneous immunotherapy (SCIT): Injections given weekly to monthly.
Sublingual immunotherapy (SLIT): Allergen tablets or drops placed under the tongue.

b) Benefits:

Long-term remission of symptoms.
Prevents development of asthma and new sensitizations.

c) Limitations:

Requires long-term adherence (3–5 years).
Risk of systemic allergic reactions.

4. Surgical Management

In selected cases with structural obstruction or complications:

Turbinate reduction for chronic nasal blockage.
Polypectomy for nasal polyps.
Endoscopic sinus surgery for chronic sinusitis.

Surgery is considered adjunctive and not a primary treatment for allergic rhinitis.

Prevention

Preventive strategies focus on early allergen exposure control and immune modulation.

Encourage breastfeeding to enhance immune tolerance in infants.
Avoid tobacco smoke exposure during pregnancy and early childhood.
Promote outdoor activities to support normal immune development.
Use HEPA filters in homes with high allergen loads.
Implement school-based awareness programs to improve early diagnosis.

Prognosis

Allergic rhinitis is a chronic condition but can be effectively controlled with proper management. Many children experience improvement with age, although some develop asthma or persistent symptoms into adulthood. Early recognition and intervention are essential for better long-term outcomes.

Quality of Life Impact

Even though allergic rhinitis is not fatal, it significantly affects:

Sleep quality leading to fatigue.
Cognitive function and school/work performance.
Social interaction due to constant sneezing or congestion.
Emotional well-being, leading to anxiety and irritability.

Comprehensive management can restore normal functioning and enhance life quality.

Recent Advances

1. Biologic Therapies

Monoclonal antibodies targeting IgE (e.g., omalizumab) and cytokines (e.g., anti-IL-5) show promising results in severe cases resistant to conventional therapy.

2. Intranasal Anticholinergics

Agents like ipratropium bromide reduce excessive nasal secretions.

3. Genetic and Molecular Research

Studies on epigenetics and gene-environment interactions are paving the way for personalized treatment.

4. Immunomodulatory Probiotics

Probiotics such as Lactobacillus and Bifidobacterium strains are being investigated for preventive and therapeutic potential.

Conclusion

Allergic rhinitis is a widespread, chronic, and often underdiagnosed allergic condition that affects individuals of all ages. Its burden extends beyond nasal symptoms, influencing overall health, emotional well-being, and productivity. Understanding its immunological mechanisms has greatly improved diagnostic and therapeutic strategies.

A multidisciplinary approach—including patient education, allergen avoidance, pharmacologic therapy, and immunotherapy—remains the cornerstone of management. Continued research into genetic factors, biologics, and preventive interventions holds promise for more personalized and long-lasting treatments.

Ultimately, early diagnosis, consistent management, and lifestyle modifications can enable patients with allergic rhinitis to lead healthy, symptom-free lives.

Allergic Rhinitis