Eosinophilic Asthma: Risk Factors and Who Is Most Affected

Eosinophilic asthma (eos asthma) is a distinct phenotype characterized by elevated eosinophils in blood, sputum, or airway tissue. Understanding who develops it helps with early recognition and targeted treatment.

Established Risk Factors

• Atopic Predisposition: Personal history of allergic rhinitis, atopic dermatitis (eczema), food allergies, or allergic conjunctivitis. The "atopic march" often progresses to eosinophilic asthma.
• Family History: First-degree relative with asthma, allergies, or eosinophilic conditions increases risk 2–3 fold. Polygenic inheritance (IL-33, TSLP, IL-5 receptor, GATA3 pathways).
• Environmental Triggers:
  • Indoor: dust mites, pet dander, cockroach, mold
  • Outdoor: pollen (trees, grasses, weeds), air pollution (PM2.5, ozone, NO2), thunderstorm asthma events
  • Occupational: isocyanates, flour dust, wood dust, latex, cleaning agents, healthcare exposures
• Obesity (BMI ≥30): Independent risk factor. Adipose tissue produces IL-6, leptin, adipokines promoting Th2 inflammation and eosinophilia. Weight loss improves control.
• Comorbidities That Amplify Risk:
  • Chronic rhinosinusitis with nasal polyps (CRSwNP) — 50%+ have eosinophilic asthma
  • GERD (reflux) — microaspiration triggers airway eosinophilia
  • Obstructive sleep apnea — intermittent hypoxia, systemic inflammation
  • Allergic bronchopulmonary aspergillosis (ABPA)
  • EGPA (Churg-Strauss) — systemic eosinophilic vasculitis
• Early Life Factors: Prematurity, RSV bronchiolitis, antibiotic exposure, C-section, formula feeding, maternal smoking—alter microbiome/immune development.
• Adult-Onset Predominance: Eosinophilic asthma more commonly begins in adulthood (30s–50s), often non-allergic, more severe, steroid-dependent.

Who Is Affected: Epidemiology

• ~40–50% of severe asthma is eosinophilic
• Slight female predominance (especially adult-onset)
• All racial/ethnic groups affected; disparities in diagnosis/access
• Non-allergic eosinophilic asthma: ~30–40% of eos asthma—no IgE sensitization, often later onset, more severe

Clinical Recognition

Consider eosinophilic asthma if:

• Adult-onset asthma, especially female
• Poor control despite moderate-high dose ICS/LABA
• Frequent exacerbations (≥2/year requiring OCS)
• Blood eosinophils ≥150–300 cells/µL (or sputum ≥2–3%)
• Coexisting CRSwNP, eosinophilic esophagitis, atopic dermatitis

Early phenotyping (blood eosinophils, FeNO, IgE, periostin) guides biologic selection and avoids years of ineffective step-up therapy. If this profile fits, ask your pulmonologist/allergist about eosinophilic asthma workup.