Asthma Phenotypes and Endotypes: A Guide to Precision Asthma Care

By Dr. Frank Hull, MD — Board-Certified Pulmonologist, Advanced Asthma Clinic, Plantation, FL | Updated June 2026

For decades, asthma was treated as a single disease. All patients received the same stepwise regimen: start with a short-acting inhaler, add an inhaled corticosteroid, escalate to combination therapy, and hope for the best. This approach left a significant number of patients — particularly those with severe, hard-to-control asthma — inadequately treated despite maximum conventional therapy.

The revolution in asthma care over the past 15 years has been the recognition that asthma is not one disease but a collection of related diseases, each with a distinct biological fingerprint. Understanding your specific asthma type — its phenotype and endotype — is now the foundation of choosing the right treatment, particularly when it comes to biologic therapies.

At Advanced Asthma Clinic in Plantation, FL, Dr. Frank Hull uses a comprehensive biomarker-driven approach to classify and treat asthma with the precision it demands.

Phenotype vs. Endotype: What Is the Difference?

These two terms are often used interchangeably, but they describe different levels of understanding:

Think of it this way: phenotype is the description, endotype is the explanation. A patient may present with the late-onset, severe asthma phenotype — and the underlying endotype could be eosinophilic T2-high disease, which is highly treatable with specific biologics. Knowing the endotype transforms treatment from guesswork into precision medicine.

The Major Asthma Phenotypes

Clinicians use phenotyping to cluster patients by shared observable features. The major clinically recognized asthma phenotypes include:

Allergic (Atopic) Asthma

The most common phenotype, especially in children and young adults. Patients have a personal or family history of atopic disease — eczema, hay fever, or food allergies — and demonstrate sensitization to environmental allergens (dust mites, pet dander, mold, pollen) via skin prick testing or specific IgE blood tests. Symptoms often worsen seasonally or with specific exposures. Most cases are T2-high endotype.

In South Florida, perennial high pollen counts, year-round mold spores, and warm humidity make allergic asthma particularly prevalent across Broward County and the surrounding region.

Non-Allergic (Intrinsic) Asthma

Asthma that is not driven by allergic sensitization. It tends to have an adult onset (typically after age 40), affects women more often than men, and may be more severe and steroid-resistant. Triggers are non-specific: cold air, exercise, respiratory infections, aspirin or NSAIDs, and airway irritants. The endotype is heterogeneous — some cases are T2-high eosinophilic; others are T2-low.

Late-Onset Asthma

By definition, asthma that appears for the first time in adulthood (age 40 or older). New-onset asthma after 40 warrants thorough evaluation to rule out alternative diagnoses including COPD, cardiac asthma, vocal cord dysfunction, and occupational asthma. When confirmed as true late-onset asthma, patients often have severe, eosinophilic disease with high biomarker burden and an excellent response to anti-IL5 biologics.

Eosinophilic Asthma

This is both a phenotype and an endotype — the term refers to asthma characterized by persistent eosinophilic airway inflammation, regardless of allergic sensitization status. Key features include:

• Blood eosinophils ≥300 cells/µL (often much higher)
• Frequent exacerbations despite inhaled corticosteroids
• May be associated with chronic rhinosinusitis with nasal polyps
• May be associated with aspirin-exacerbated respiratory disease (AERD / Samter's triad)

Eosinophilic asthma responds exceptionally well to anti-IL5 biologics (mepolizumab, reslizumab, benralizumab) and to dupilumab (anti-IL4Rα).

Obesity-Related Asthma

A distinct phenotype with unique features: symptoms are driven partly by mechanical restriction of lung expansion, partly by adipokine-mediated airway inflammation, and partly by increased gastroesophageal reflux. Patients tend to have a T2-low endotype, meaning standard biologics targeting IgE or IL-5 may be less effective. Weight loss through lifestyle modification or bariatric surgery can produce significant asthma improvement — sometimes more than medications alone.

Exercise-Induced Asthma / EIB

Triggered by vigorous physical activity, driven by airway drying and osmotic stress. May occur as the only asthma manifestation or alongside persistent asthma. See our dedicated article: Exercise-Induced Bronchoconstriction: Diagnosis and Treatment.

Occupational Asthma

Caused or worsened by workplace exposures to sensitizing agents or high-level irritants. Represents approximately 15% of adult-onset asthma. For a full overview, see: Occupational Asthma: Causes, Diagnosis, and Workplace Rights.

The Core Endotypes: T2-High vs. T2-Low Asthma

At the molecular level, the most clinically important distinction is between type 2 (T2)-high and type 2-low asthma. This determines which biologic pathways are active — and therefore which treatments will work.

T2-High Asthma

T2-high asthma is driven by type 2 immune inflammation, primarily mediated by three cytokines:

• IL-4: Promotes B-cell class switching to produce IgE; drives Th2 differentiation
• IL-5: The master regulator of eosinophil production, maturation, and survival
• IL-13: Drives mucus hypersecretion, airway hyperresponsiveness, and subepithelial fibrosis

These cytokines are released by Th2 CD4+ T cells and type 2 innate lymphoid cells (ILC2s), which are activated by epithelial alarmins — TSLP, IL-33, and IL-25 — released in response to allergens, viruses, and irritants.

T2-high biomarkers include:

• Blood eosinophils ≥150–300 cells/µL
• FeNO (fractional exhaled nitric oxide) ≥25 ppb
• Elevated total serum IgE or allergen-specific IgE
• Sputum eosinophils ≥3% (specialized testing)

T2-high asthma is the target of all currently FDA-approved biologics for asthma. Approximately 50–60% of severe asthma patients have a T2-high profile.

T2-Low Asthma

T2-low asthma lacks the eosinophilic signature. Airway inflammation is driven by alternative mechanisms, including:

• Neutrophilic inflammation: Associated with air pollution exposure, smoking, recurrent infections, obesity, and in some cases corticosteroid use itself. May respond to macrolide antibiotics (azithromycin).
• Paucigranulocytic inflammation: Few inflammatory cells in airway secretions; driven more by airway smooth muscle hyperreactivity than inflammation. Often the most difficult to treat.
• Mixed granulocytic: Both eosinophils and neutrophils present, often in patients with more severe disease.

T2-low asthma is the unmet need in severe asthma research. Current clinical trials are actively targeting novel pathways including the Th17/IL-17 axis, PDE4 inhibition, and targeted approaches for neutrophilic disease. Learn about clinical trial opportunities at our affiliated research site.

Biomarkers Used to Classify Your Asthma

Phenotyping and endotyping rely on a set of readily available laboratory and clinical tests. Dr. Hull incorporates the following in the evaluation of moderate-to-severe asthma:

Most patients require at least two or three of these biomarkers measured at steady state — ideally while not taking oral corticosteroids, which suppress eosinophil counts and can mask the true inflammatory burden.

Why Phenotyping Matters: Matching Biologic to Endotype

The practical payoff of phenotyping and endotyping is selecting the right biologic. Each FDA-approved biologic for severe asthma targets a specific molecular pathway. Matching the drug to the active pathway in your airway is what produces the dramatic reductions in exacerbation rates — often 50–70% fewer severe asthma attacks — seen in clinical trials.

Selecting among these six agents requires integrating your biomarker profile with your clinical history, comorbidities (particularly nasal polyps, atopic dermatitis, AERD), exacerbation frequency, and current medication burden. There is no single "best" biologic — the right one is the one matched to your endotype.

The T2 Overlap: Asthma and Its Inflammatory Comorbidities

Many patients with severe eosinophilic asthma carry a cluster of T2-driven comorbidities that share the same underlying inflammatory pathway:

• Chronic rhinosinusitis with nasal polyps (CRSwNP): Bilateral nasal polyps, chronic nasal congestion, smell loss
• Aspirin-exacerbated respiratory disease (AERD / Samter's Triad): Asthma + nasal polyps + NSAID intolerance
• Atopic dermatitis (eczema): IL-4/IL-13-driven skin inflammation
• Eosinophilic esophagitis (EoE): Eosinophilic inflammation of the esophagus causing swallowing difficulty
• Allergic bronchopulmonary aspergillosis (ABPA): IgE-mediated fungal sensitization causing recurrent lung infiltrates

When a patient presents with two or more of these conditions simultaneously, it strongly confirms a T2-high endotype and typically points toward broad T2 pathway blockade — dupilumab or tezepelumab — rather than a narrowly targeted anti-IL5 agent.

Phenotype Can Change: The Importance of Ongoing Reassessment

A critical concept often missed: asthma phenotype and endotype are not fixed for life. Several clinical scenarios cause shifts:

• Aging: Childhood allergic asthma may evolve toward non-allergic, late-onset eosinophilic disease with less IgE dependence in adulthood
• Hormonal changes: Menopause, pregnancy, and hormonal contraceptives can shift the inflammatory balance — see asthma and hormones
• Weight gain: Significant obesity can convert a T2-high patient to a mixed or predominantly T2-low phenotype, reducing biologic efficacy
• Biologic therapy itself: Sustained eosinophil suppression with anti-IL5 agents can occasionally unmask previously hidden neutrophilic inflammation
• Respiratory infections: Viral infections can shift inflammatory patterns transiently; chronic bacterial infections may drive neutrophilic airway remodeling

For this reason, Dr. Hull reassesses biomarkers at regular intervals — typically every 6–12 months in patients receiving biologic therapy — to confirm the treatment remains aligned with the current disease state.

How We Evaluate Your Asthma Phenotype at Advanced Asthma Clinic

A typical phenotyping evaluation at our Plantation, FL clinic includes:

1. Detailed clinical history: Onset age, trigger patterns, seasonal variation, atopic history, family history, occupational exposures, medication response history
2. Comprehensive lung function testing: Spirometry, bronchodilator reversibility, lung volumes, diffusion capacity — see Lung Function Testing at Advanced Asthma Clinic
3. FeNO measurement: A simple, non-invasive, 10-second breath test performed in office
4. Biomarker blood panel: Blood eosinophils, total IgE, complete blood count, and periostin when indicated
5. Allergen skin testing or specific IgE panel: To confirm or exclude allergic sensitization
6. Comorbidity screen: CT sinuses (if nasal polyps suspected), GERD evaluation, obesity assessment, anxiety and depression screening
7. Medication review: Inhaler technique assessment, adherence evaluation, step-therapy optimization before biologics are considered

This process typically spans one to two clinic visits, after which Dr. Hull presents a clear phenotype classification, biologic candidacy assessment, and individualized management plan. Serving patients from Plantation, Fort Lauderdale, Davie, Miramar, Hollywood, and all of Broward County.

Clinical Trials for Specific Asthma Phenotypes

Advanced asthma research is rapidly advancing for both T2-high and T2-low disease. Through our affiliated Lung Research Florida site, Dr. Hull conducts clinical trials targeting specific asthma phenotypes, including:

• Severe eosinophilic asthma (T2-high): Next-generation biologic therapy evaluated for patients with persistent eosinophilia despite existing treatments (ages 18–75)
• COPD with eosinophilic overlap: Anti-IL-33 therapy for patients aged 40–80 with eosinophilia and airflow limitation
• Chronic cough: P2X3 receptor antagonist for cough hypersensitivity syndrome (ages 18–80)
• Bronchiectasis: Investigational bispecific antibody therapy (ages 18–85)

Participation may provide access to investigational therapies not yet commercially available, often at no cost to the participant. Learn more about our current clinical trials or call Lung Research Florida at (954) 520-7296 x1 to discuss eligibility.

Frequently Asked Questions

What is the difference between an asthma phenotype and an endotype?

A phenotype describes observable characteristics — what asthma looks like clinically (allergic vs. non-allergic, early-onset vs. late-onset). An endotype describes the underlying biological mechanism — what is driving the disease at the molecular level (T2-high eosinophilic vs. T2-low neutrophilic). Endotyping is the key to selecting the right biologic therapy.

What is T2-high asthma?

T2-high asthma is driven by type 2 immune inflammation mediated by cytokines IL-4, IL-5, and IL-13. It is characterized by elevated blood eosinophils (typically ≥150–300 cells/µL), elevated FeNO (≥25 ppb), and often elevated total IgE. All currently FDA-approved biologics for severe asthma target T2-high pathways.

How is eosinophilic asthma diagnosed?

Eosinophilic asthma is identified through a simple blood test measuring blood eosinophil counts. Counts ≥300 cells/µL are a strong signal; ≥150 cells/µL is relevant for biologic eligibility. FeNO ≥25 ppb also suggests eosinophilic airway inflammation. Sputum eosinophil counts ≥3% are the most direct measure but require specialized testing.

Which biologic is right for my asthma?

Biologic selection depends on your specific biomarker profile and clinical picture. Anti-IgE (omalizumab) suits allergic, IgE-driven asthma. Anti-IL5 agents (mepolizumab, reslizumab, benralizumab) target eosinophilic disease. Dupilumab (anti-IL4Rα) addresses T2-high mechanisms broadly. Tezepelumab (anti-TSLP) has the broadest indication, working across most T2-high phenotypes regardless of eosinophil count. A biomarker-guided evaluation with Dr. Hull identifies the best fit for you.

What if my asthma is T2-low?

T2-low asthma is currently harder to target with biologics. Treatment focuses on optimized ICS-LABA therapy, comorbidity management (weight, GERD, anxiety), and potential add-on therapies such as LAMAs or macrolide antibiotics in neutrophilic disease. Clinical trials are actively investigating new pathways — ask about current research opportunities at Advanced Asthma Clinic.

Does asthma phenotype stay the same over time?

No — asthma phenotype and endotype can shift with aging, hormonal changes, weight gain, new exposures, or biologic therapy. Regular biomarker reassessment (at least annually for patients on biologics) is important to ensure treatment remains matched to the current disease state.

This article is for informational purposes only and does not constitute medical advice. Always consult your physician for diagnosis and personalized treatment recommendations.