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 (year-round), seasonal, or episodic depending on the pattern of allergen exposure. 1
Primary Causes
Perennial Allergens
- Dust mites - a major cause of year-round symptoms in many climates 1
- Animal dander - particularly from household pets like cats and dogs 1
- Indoor mold - can persist throughout the year in damp environments 1
- Cockroach allergens - common in urban environments 2
- Occupational allergens - various workplace substances that cause persistent symptoms 1, 3
Seasonal Allergens
- Tree pollens - typically prevalent in spring 1
- Grass pollens - most common in late spring and summer 1, 4
- Weed pollens (especially ragweed) - predominant in fall 1, 5
- Outdoor molds - levels fluctuate seasonally with higher concentrations in warm, humid weather 1
Episodic Allergens
- Exposures to allergens not normally encountered in the patient's environment (e.g., visiting a home with pets) 1
Risk Factors
Genetic Factors
- Family history of atopy - significantly increases risk, especially when both parents have atopic conditions 2
- Elevated serum IgE levels in early childhood (>100 IU/mL before age 6) 2
Environmental Factors
- Early and repeated exposure to specific allergens leading to sensitization 2
- Higher socioeconomic status 2
- Heavy tobacco smoke exposure in early childhood 2
- Urban living with increased pollution exposure 2, 4
Demographic Factors
- Age - 80% of cases develop before age 20 2
- Race - increased prevalence in non-white populations 2
- Birth order - first-born children have higher risk 2
Pathophysiology
The allergic response in chronic allergic rhinitis involves:
- Initial allergen exposure leading to sensitization with production of allergen-specific IgE antibodies 4
- Re-exposure to allergens causing cross-linking of IgE on mast cells and basophils 1, 4
- Release of inflammatory mediators including histamine, leukotrienes, and cytokines 1
- Early-phase response characterized by sneezing, itching, and rhinorrhea 1
- Late-phase response dominated by nasal congestion due to inflammatory cell recruitment 1
Clinical Implications
- Persistent symptoms (>4 days/week and >4 weeks/year) significantly impact quality of life, sleep, work productivity, and school performance 1, 6
- Chronic allergic rhinitis is associated with comorbidities including asthma, sinusitis, and sleep disorders 4, 6
- Sleep disruption from nasal obstruction can lead to fatigue, irritability, memory deficits, and depression 6
Common Pitfalls in Diagnosis
- Failing to distinguish between allergic and non-allergic rhinitis, which have different causes and treatment approaches 2
- Not recognizing mixed rhinitis, affecting 44-87% of patients with allergic rhinitis 2
- Overlooking occupational causes in patients with work-related symptom patterns 3
- Misattributing symptoms to infection rather than allergy in cases of persistent rhinitis 1, 4
Understanding these causes is essential for implementing appropriate avoidance measures and selecting optimal pharmacologic therapy for chronic allergic rhinitis.