What causes Chronic Allergic Rhinitis (AR)?

Causes of Chronic Allergic Rhinitis

Chronic allergic rhinitis is primarily caused by an IgE-mediated inflammatory response of the nasal mucous membranes after exposure to inhaled allergens, which can be classified as perennial, seasonal, or episodic depending on the pattern of allergen exposure. 1

Primary Allergens Causing Chronic AR

Perennial (Year-Round) Allergens

• Dust mites are a major cause of perennial allergic rhinitis in many climates 1
• Animal dander, particularly from household pets like cats and dogs, is a common perennial allergen 1
• Indoor mold persists throughout the year in damp environments and triggers chronic symptoms 1
• Certain occupational allergens can cause year-round symptoms in affected workers 2

Seasonal Allergens

• Tree pollens (typically prevalent in spring) 1
• Grass pollens (most common in late spring and summer) 1
• Weed pollens, especially ragweed (predominant in fall) 1
• Outdoor molds (fluctuate seasonally, with higher concentrations in warm, humid weather) 1

Episodic Allergens

• Allergens not normally part of an individual's environment (e.g., visiting a home with pets) 3

Pathophysiological Mechanism

• The allergic response involves disruption of the epithelial barrier allowing allergens to penetrate the nasal mucosa 4
• This triggers a T-helper type 2 inflammatory response and production of allergen-specific IgE 4
• Upon re-exposure to allergens, inflammatory mediators are released, including histamine, leukotrienes, and cytokines 1
• The early-phase response causes sneezing, itching, and rhinorrhea, while the late-phase response leads to nasal congestion due to inflammatory cell recruitment 1

Risk Factors for Developing Chronic AR

Genetic and Biological Factors

• Family history of atopy significantly increases risk, especially when both parents have atopic conditions 1, 5
• Elevated serum IgE levels in early childhood (>100 IU/mL before age 6) 5
• Positive allergy skin prick test indicating existing sensitization 5

Environmental Factors

• Early and repeated exposure to specific allergens leading to sensitization 5
• Higher socioeconomic status 1, 5
• Heavy tobacco smoke exposure in early childhood 1, 5
• Urban living with increased pollution exposure 1

Demographic Factors

• Age: 80% of cases develop before age 20 5
• Seasonal allergic rhinitis typically develops between ages 2-7 years 5
• Perennial allergic rhinitis may present at a very early age 5

Classification by Symptom Pattern

• Intermittent allergic rhinitis: symptoms occur <4 days per week or <4 weeks per year 3
• Persistent allergic rhinitis: symptoms occur >4 days per week and >4 weeks per year 3

Clinical Implications

• Persistent symptoms significantly impact quality of life, sleep, work productivity, and school performance 1
• AR is associated with comorbidities including asthma, eczema, chronic sinusitis, and headaches 1, 4
• AR generates $2-5 billion in direct health expenditures annually in the United States 3

Common Pitfalls in Diagnosis

• Failing to distinguish between allergic and non-allergic rhinitis, which have different causes and risk profiles 5
• Not recognizing mixed rhinitis, which affects 44-87% of patients with allergic rhinitis 5
• Overlooking occupational causes that may include both IgE-mediated allergic occupational rhinitis and irritant-induced rhinitis 2