Eosinophilic asthma is a subtype of asthma driven by high levels of eosinophils, a type of white blood cell that causes persistent inflammation in the airways. It accounts for a large share of severe asthma cases, with data from the International Severe Asthma Registry across 11 countries showing that over 80% of severe asthma patients have an eosinophilic phenotype. Unlike the childhood-onset, allergy-triggered asthma most people picture, eosinophilic asthma often develops in adulthood and can be difficult to control with standard inhalers alone.
How Eosinophils Damage the Airways
In a healthy immune system, eosinophils help fight parasites and play a minor role in immune regulation. In eosinophilic asthma, they accumulate in the airway lining and release a cocktail of toxic proteins and inflammatory signals that damage the tissue. These proteins irritate and injure the cells lining your airways, triggering a cycle of damage, attempted repair, and structural remodeling that gradually thickens the airway walls. Over time, this remodeling makes the airways narrower and more reactive to triggers, which is why symptoms tend to worsen over years if the underlying inflammation isn’t addressed.
The process is orchestrated by a specific branch of the immune system sometimes called the “type 2” or T2-high pathway. In people with allergic eosinophilic asthma, immune cells called Th2 cells recognize an allergen and release signaling molecules (particularly IL-4, IL-5, and IL-13) that recruit eosinophils to the lungs and stimulate excess mucus production. But eosinophilic asthma doesn’t always involve allergies. In non-allergic cases, a different set of immune cells called innate lymphoid cells drives the same eosinophil buildup without any identifiable allergen. This is an important distinction: you can have eosinophilic asthma with no positive allergy tests whatsoever.
What It Feels Like
The core symptoms overlap with other forms of asthma: wheezing, shortness of breath, chest tightness, and coughing. What sets eosinophilic asthma apart is the pattern. It tends to appear in adulthood rather than childhood, and flare-ups (exacerbations) are often more frequent and more severe. Many people with this subtype find their symptoms respond only partially to standard inhaled corticosteroids, leading to repeated courses of oral steroids and frustrating cycles of partial control followed by another flare.
Several comorbidities cluster with eosinophilic asthma and can be clues to the diagnosis. Chronic rhinosinusitis with nasal polyps is one of the most common, creating a combination of constant nasal congestion, reduced sense of smell, and difficult-to-control asthma. Other associated conditions include aspirin-exacerbated respiratory disease, eosinophilic esophagitis, and atopic dermatitis. If you have asthma alongside one or more of these, the eosinophilic subtype becomes more likely.
How It’s Diagnosed
Eosinophilic asthma is identified through a combination of blood tests and breathing tests rather than a single definitive marker. The most accessible test is a simple blood draw measuring your eosinophil count. A level above 300 cells per microliter is a strong indicator and predicts both a higher risk of exacerbations and a good response to corticosteroid treatment. A lower threshold of 150 cells per microliter is used to identify patients likely to benefit from biologic therapies. Because eosinophil counts fluctuate, doctors typically look at the highest recorded value rather than a single reading.
Another useful tool is a FeNO test, which measures nitric oxide in your exhaled breath. A reading of 25 parts per billion or higher in adults signals eosinophilic airway inflammation. The test is quick, noninvasive, and can be done in a clinic visit. Using FeNO alongside blood eosinophil counts gives a more complete picture than either test alone. In some cases, doctors may also analyze a sputum sample to directly count eosinophils in airway mucus, though this is less commonly available.
Why Standard Inhalers Often Aren’t Enough
Inhaled corticosteroids are the backbone of asthma treatment, and they do work for eosinophilic asthma to a degree. Eosinophilic inflammation is generally more responsive to steroids than non-eosinophilic forms. The problem is that many people with this subtype have severe, persistent inflammation that inhaled steroids can’t fully suppress, especially at the doses considered safe for long-term use. This leads to a pattern of needing repeated bursts of oral corticosteroids to regain control, which over months and years causes significant side effects: weight gain, bone thinning, elevated blood sugar, and immune suppression.
This treatment gap is precisely why biologic therapies have transformed management of severe eosinophilic asthma over the past decade.
Biologic Treatments
Biologics are injectable medications that target specific molecules in the inflammatory chain rather than broadly suppressing the immune system the way steroids do. For eosinophilic asthma, the main targets are IL-5 (the key signal that produces and activates eosinophils) and IL-4/IL-13 (signals that drive mucus production and airway remodeling).
IL-5 Targeted Therapies
Mepolizumab is the most widely used. It blocks IL-5 from reaching eosinophils, and in clinical trials it reduced asthma exacerbations by 53%. It’s approved for patients 6 and older with blood eosinophils at or above 150 cells per microliter, given as an injection every four weeks. Benralizumab takes a different approach: instead of blocking the IL-5 signal, it targets the receptor on eosinophils and triggers their destruction directly. This led to a 51% reduction in exacerbations and, notably, a 75% reduction in oral corticosteroid use. After three initial monthly doses, it’s given every eight weeks. Reslizumab, administered by IV infusion every four weeks, works best in patients with eosinophil counts above 400 cells per microliter and has shown up to a 92% reduction in circulating eosinophils.
IL-4/IL-13 Targeted Therapies
Dupilumab blocks both IL-4 and IL-13 signaling simultaneously, addressing a broader portion of the inflammatory cascade. This makes it particularly useful for patients who have overlapping conditions like atopic dermatitis or nasal polyps alongside their asthma, since those same signals drive inflammation across multiple organs. Several newer therapies targeting IL-13 alone or the upstream trigger IL-33 are in development or recently approved for related conditions.
IgE Targeted Therapy
For patients whose eosinophilic asthma has a clear allergic component, omalizumab blocks IgE, the antibody responsible for allergic reactions. It’s been available the longest and remains an option when allergy is a prominent driver.
The choice among biologics depends on your specific blood markers, symptom pattern, and comorbidities. Most people notice a reduction in flare-ups within the first few months and are able to taper down or eliminate oral steroid use over time. These medications don’t cure eosinophilic asthma, but they can shift it from poorly controlled and steroid-dependent to manageable with fewer side effects.
Living With Eosinophilic Asthma
Getting the right diagnosis matters more with this subtype than with many forms of asthma, because the treatment path changes significantly once eosinophilic inflammation is confirmed. If your asthma was diagnosed years ago and you’re still experiencing frequent flare-ups despite using inhalers correctly, asking about blood eosinophil testing and FeNO is a reasonable next step. Many people spend years on escalating steroid doses before being identified as candidates for biologics.
Tracking your triggers remains important, though in non-allergic eosinophilic asthma, traditional avoidance strategies like removing dust mites or pets may not help much. Respiratory infections, air pollution, and weather changes tend to be more relevant triggers. Nasal polyps, if present, often need their own treatment plan alongside asthma management, and several of the newer biologics address both conditions simultaneously.