Last updated: June 29, 2023

Summarytoggle arrow icon

Asthma is a chronic inflammatory disease of the respiratory system characterized by bronchial hyperresponsiveness, episodic acute asthma exacerbations, and reversible airflow obstruction. Allergic (extrinsic) asthma usually develops in childhood and is triggered by allergens such as pollen, dust mites, and certain foods. Nonallergic (environmental or intrinsic) asthma usually develops in patients over the age of forty and can have various triggers, such as cold air, medications (e.g., aspirin), exercise, and viral infections. The cardinal symptoms of asthma are intermittent dyspnea, cough, and high-pitched expiratory wheeze. Symptoms remit in response to antiasthmatic medications or resolve spontaneously upon removal of the trigger. In a patient with typical clinical features of asthma, diagnosis is confirmed by demonstrating reversible bronchial obstruction on pulmonary function tests. Additional tests may be required to evaluate for asthma triggers and comorbidities that increase the risk of acute exacerbations. Treatment regimens differ based on the severity of asthma but primarily consist of different combinations of beta-2 agonists and inhaled corticosteroids (ICS). Systemic corticosteroids are usually reserved for patients with severe persistent asthma. To achieve symptomatic control and minimize the risk of exacerbations, comorbidities should be managed and exposure to asthma triggers minimized. Follow-ups are essential to monitor the response to therapy and to adjust treatment regimens in a stepwise manner.

Acute asthma exacerbations” and “Exercise-induced bronchoconstriction” are discussed in their own articles.

Definitionstoggle arrow icon

  • Asthma: a chronic inflammatory disease of the respiratory system characterized by bronchial hyperresponsiveness, episodic exacerbation (asthma attacks), and reversible airflow obstruction; manifests with reversible cough, wheezing, and dyspnea
  • Acute asthma exacerbation: a reversible worsening of the clinical features of asthma that develops over a short period of time and can progress to life-threatening asthma; may be the first manifestation of asthma in some patients
  • Allergic asthma: the most common type of asthma; begins with intermittent symptoms in childhood and is usually associated with atopy (e.g., eczema, rhinitis) and a good response to treatment
  • Nonallergic asthma: an uncommon type of asthma that is not related to atopy and is typically associated with a poor response to standard treatment (e.g., ICS)
  • See also “Subtypes and variants.”

Epidemiologytoggle arrow icon

  • Prevalence
    • 5–10% of the US population
    • More common in black than white patients
    • For unknown reasons, the prevalence of asthma has been increasing over the past 20 years. [1]
  • Sex: differs depending on age of onset
    • > in patients < 18 years
    • > in patients > 18 years
  • Age of onset


Epidemiological data refers to the US, unless otherwise specified.

Etiologytoggle arrow icon

Asthma triggers
Allergic asthma
(extrinsic asthma)
Nonallergic asthma
(intrinsic asthma)

Childhood exposure to second-hand smoke increases the risk of developing asthma.

Pathophysiologytoggle arrow icon

Common underlying pathophysiology

Asthma is an inflammatory disease driven by T-helper type 2 cells (Th2-cell) that manifests in individuals with a genetic predisposition. It consists of the following three pathophysiologic processes:

  1. Bronchial hyperresponsiveness
  2. Bronchial inflammation
  3. Endobronchial obstruction caused by:

Type-specific pathophysiology

Clinical featurestoggle arrow icon

Characteristic examination findings may not be present between episodes of asthma exacerbation!

Subtypes and variantstoggle arrow icon

  • Adult-onset asthma: an uncommon phenotype in which patients present with symptoms for the first time in adulthood; more likely to be nonallergic and involves a poor response to standard treatment
  • Cough variant asthma: : a form of asthma in which the predominant symptom is chronic dry cough, without other characteristic symptoms of asthma, e.g., wheeze, congestion, dyspnea (see also “Cough”)
  • Exercise-induced bronchoconstriction: covered separately in its own article

Asthma-COPD overlap

Asthma-COPD overlap is the presence of features of both asthma and COPD in an individual. [6][7][8]

Asthma-COPD overlap is not a distinct disease entity, but a term used to describe a heterogeneous category of patients with features of both diseases. [7][9]

Clinical features [7]

  • Chronic presentation, most commonly with intermittent or episodic symptoms
  • Common symptoms include cough, SOB, chest tightness, and wheezing.
  • Symptoms may:
  • May develop in patients with a known history of asthma or COPD
  • See also “Comparison of asthma and COPD.”

Patients with asthma-COPD overlap experience more symptoms, more frequent exacerbations, and higher mortality than patients with either asthma or COPD alone. [7]

Diagnostics [6][7]

Do not wait for diagnostic confirmation before initiating treatment for asthma in patients with suspected asthma-COPD overlap; untreated patients are at risk of life-threatening acute asthma attacks. [7]

Management [7]

  • Refer to a pulmonologist for any of the following:
    • Presence of symptoms atypical of asthma or COPD
    • Suspected chronic airway disease but minimal symptoms of asthma or COPD
    • Uncertain diagnosis or suspicion of an alternative diagnosis
    • Comorbidities causing difficulty with work-up or management
  • All other patients

Patients with concurrent asthma and COPD symptoms should never be treated with a LABA or LAMA alone; these must always be given in conjunction with an ICS. [7]

Diagnosticstoggle arrow icon

General principles [3][11][12]

Pulmonary function testing [3][11][12]

  • Characteristic findings (observable using any of the PFT modalities described below)
Diagnostic testing in asthma [11][12]
PFT modality Supportive findings Test characteristics
Peak flow meter (PFM)
  • Portable device
  • Allows rapid serial measurement of PEFR
  • Less accurate than spirometry
  • FEV1
  • FEV1/FVC ratio
  • Excessive variability of FEV1 or FEV1/FVC:
    • Between visits
    • In response to therapy
    • In response to physiological challenges
  • Greater accuracy than PFM
  • Can identify baseline parameters (“personal best”)
  • Difficult to perform compared to PFM
  • Greater logistical challenge
Bronchial reversibility tests
  • Added to spirometry or PFM as part of the first-line investigations to assess reversibility or responsiveness of airflow limitation to treatment
Bronchial provocation tests

A normal FEV1 in a patient who is symptomatic at the time of testing makes a diagnosis of asthma less likely.

Asthma and COPD both cause an obstructive pattern on PFTs. Complete reversibility of bronchial obstruction after bronchodilator administration rules out COPD.

Adjunctive studies

Differential diagnosestoggle arrow icon

The main alternate obstructive lung disease to consider is COPD. The main differentiating features are detailed below. See also “Differential diagnosis of chronic cough,” “Differential diagnosis of dyspnea,” “Differential diagnosis of acute asthma”, and “Wheezing in children” for other conditions that can mimic asthma.

Asthma vs. COPD

Comparison of asthma and COPD

Asthma COPD
Age at diagnosis
  • Typically > 40 years old
  • Allergic and nonallergic (see “Etiology” above)
  • Cigarette consumption (90% of cases)
Clinical presentation
  • Insidious onset
  • Chronic progression over years
Bronchial obstruction
  • Reversible
  • Persistent


Consider allergic bronchopulmonary aspergillosis if respiratory symptoms worsen and/or features of bronchiectasis develop despite asthma treatment.

Reactive airway disease [15]

  • Description
    • A nonspecific term used to describe symptoms and findings that are similar to those of asthma (e.g., wheezing, coughing, airway sensitivity)
    • Underlying conditions include asthma, pneumonia, COPD, and/or bronchitis
    • Most commonly used in pediatric settings when asthma is suspected, but not yet confirmed
  • Clinical features: wheezing, coughing, dyspnea, and/or sputum production

Ascription of the label “Reactive airway disease” may prevent a thorough workup of the actual underlying condition and/or lead to the prescription of ineffective medication.

The differential diagnoses listed here are not exhaustive.

Treatmenttoggle arrow icon

General principles [3][11][12]

The key to long-term asthma management is a continuous cycle of clinical assessment and treatment adjustment.

Approach [3][11][12]

  1. Confirm diagnosis of asthma.
  2. Assess severity (see “Classification of asthma severity”).
  3. Initiate antiasthmatic medication based on severity.
  4. Manage comorbidities; reduce exposure to asthma triggers (see “Adjunctive therapy”).
  5. Monitor response to therapy.
  6. Adjust treatment (step up or step down) based on response to therapy.
  7. Schedule frequent follow-ups.

Long-term follow-up and reassessment of asthma symptom control are recommended every 1–6 months.

Assessment of severitytoggle arrow icon

  • The National Asthma Education and Prevention Program (NAEPP) guidelines classify asthma severity as intermittent or persistent in individuals who have not yet been initiated on long-term therapy based on the following: [3][11]
    • Symptom severity
    • Degree of impairment in lung function
    • Frequency and risk of exacerbations
  • The 2020 Global Initiative for Asthma (GINA) guidelines classify severity into well-controlled, partly-controlled, and uncontrolled based on the minimum level of long-term treatment required to achieve symptom control (not detailed here). [3][12]

Classification of asthma severity in adults and children ≥ 12 years of age (NAEPP) [3][11]

The most severe category of any feature determines the severity.

Class Symptom severity Lung function Exacerbations requiring systemic corticosteroids
Intermittent asthma
  • Symptom frequency: ≤ 2/week
  • Waking up because of symptoms: ≤ 2/month
  • No interference with daily activities
  • Use of SABA ≤ 2 days/week
  • Normal between exacerbations
  • FEV1 > 80% predicted
  • Normal FEV1/FVC
  • ≤ 1/year
Persistent asthma Mild persistent asthma
  • Symptom frequency: > 2/week (but not on the same day)
  • Waking up because of symptoms: 3–4/month
  • Use of SABA > 2 days/week
  • Minor limitation of daily activities
  • ≥ 2/year
Moderate persistent asthma
  • Symptom frequency: daily
  • Waking up because of symptoms: > 1/week (but not consecutively)
  • Some limitation of daily activities
  • Daily use of SABA
Severe persistent asthma
  • Daily symptoms throughout the day
  • Waking up because of symptoms: every night
  • Extreme limitation of daily activities
  • Use of SABA several times a day

Stepwise treatmenttoggle arrow icon

  • Different combinations of daily and rescue therapies are given in a stepwise fashion until symptoms are controlled. [3][11]
  • In treatment-naive patients, the initial treatment regimen should be guided by the severity class of asthma, clinical judgment, and patient preference.
  • Consult asthma specialists for treatment of step 4 and higher; consider specialist consultation for step 3 treatment. [11]
  • The recommendations here are consistent with the 2020 NAEPP guidelines; in areas in which they differ, the 2020 GINA guideline recommendations are also discussed.
  • Treatment of patients ≥ 12 years is detailed here; regimens differ according to the patient's age (see “Tips & links” for guidance on management of asthma in infants and children < 12 years of age).

Stepwise pharmacological treatment of chronic asthma in adults and children ≥ 12 years old (NAEPP)
See “Overview of asthma medications” for dosages. [3][11][12]

Treatment steps

Daily therapy

Single inhalers are preferred for combination medications.

Rescue inhaler (as needed)

Step 1 (intermittent asthma)

  • None [16][17][18]

Step 2 (mild persistent asthma)


Step 3 (moderate persistent asthma)



Step 4 (moderate to severe persistent asthma)


Step 5 (severe persistent asthma)

  • Medium- to high-dose ICS-LABA
  • High-dose ICS, PLUS LTRA
  • Consider adding immunotherapy.

Step 6 (severe persistent asthma)

  • Assess response to therapy in 2–6 weeks
  • Good response for ≥ 3 consecutive months: Consider a gradual decrease in pharmacotherapy (step down).
  • Inadequate response
    • Assess treatment adherence, inhaler technique.
    • Manage comorbidities and environmental factors (see “Adjunctive therapy” below).
    • Consider advancing treatment to the next step (step up).

Any change in treatment regimen should be monitored closely with regular follow-ups.

Antiasthmatic medicationstoggle arrow icon

General principles [3][11][12]

Commonly used medications [3][11][12]

Overview of commonly used asthma medications [3][11]

Dosages detailed here are for adults or children ≥ 12 years of age (unless specified)
(DPI: dry powdered inhaler; MDI: metered dose inhaler)

Class Examples Mechanism and uses Adverse effects Contraindications Interactions
Short-acting beta-2 agonists (SABA)
Long-acting beta-2 agonists (LABA)
Inhaled corticosteroids (ICS) [3]
Oral corticosteroids

ICS-LABA (combination inhaled corticosteroid and long-acting beta-2 agonist)

  • Combination of action of ICS plus bronchodilation
  • Dual use: long-term maintenance PLUS reliever for adolescents and adults
Leukotriene receptor antagonists (LTRAs)
  • Montelukast
  • Zafirlukast
  • Hypersensitivity
  • No major interactions
Long-acting muscarinic antagonists (LAMA)
Short-acting muscarinic antagonists (SAMA)

Inhaled corticosteroids do not take full effect until they have been used for approx. 1 week.

Additional medications

These medications are not commonly used in clinical practice. They are typically reserved for special cases under the guidance of a specialist.

Overview of additional asthma drugs
Agents Indications Mechanism of action Adverse effects Contraindications Interactions
Leukotriene pathway modifiers (e.g., zileuton) [19]
  • Hypersensitivity
  • Liver disease
Mast cell stabilizers (chromones; e.g., cromolyn sodium, nedocromil sodium) [20]
  • Preventive treatment prior to exercise
  • Prevent release of inflammatory mediators from mast cells

  • Throat irritation, cough
  • Hypersensitivity
  • No data available
Methylxanthines (e.g., theophylline)
  • Limited use

Anti-IgE antibodies (omalizumab) [21]

  • Select cases of severe asthma
  • Hypersensitivity
  • No data available
IL-5 antibodies (e.g., mepolizumab, reslizumab,benralizumab) [22]
  • Refractory severe eosinophilic asthma

Theophylline is no longer routinely prescribed due to the risk of toxicity. It is used solely as an adjunctive or alternative therapy.

The following drugs are not effective during an acute asthma attack: LABAs, leukotriene pathway modifiers, theophylline, mast-cell stabilizers, biological agents!

Adjunctive therapytoggle arrow icon

These measures should be optimized in all patients to reduce antiasthmatic medication requirements and decrease the frequency of acute asthma exacerbations. [3][11][12]

Controlling modifiable risk factors (e.g., smoking cessation) and comorbidities (e.g., GERD, sinusitis) can lead to better symptom control, often allowing for a step down in treatment.

Special patient groupstoggle arrow icon

  • Asthma in pregnancy
    • Asthma symptoms may be worse, better, or unchanged during pregnancy.
    • Same stepwise management as with other patients
    • Inhalation treatments preferred
    • Poorly managed asthma can increase the risk of pregnancy complications (e.g., preeclampsia, premature birth, congenital abnormalities).
    • Monthly monitoring of asthma is recommended.
  • Children under 5 years of age
    • Asthma in patients under 5 years of age is challenging to diagnose and is often underdiagnosed, as children in this age group are not typically able to adequately perform the spirometric maneuvers.
    • Regimens containing corticosteroids are preferred as initial therapy in infants and young children; see “Tips & links” for details on treatment regimens and dosages. [11]
    • Young children (< 5 years) may require nebulizers because of difficulty using inhalers. [3]

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Referencestoggle arrow icon

  1. $Expert Panel Report 3: Guidelines for the Diagnosis and Management of Asthma, Full Report 2007.
  2. Global strategy for asthma management and prevention (2020 update). Updated: April 1, 2020. Accessed: August 10, 2020.
  3. Cloutier MM, Dixon AE, Krishnan JA, Lemanske RF, Pace W, Schatz M. Managing Asthma in Adolescents and Adults. JAMA. 2020; 324 (22): p.2301.doi: 10.1001/jama.2020.21974 . | Open in Read by QxMD
  4. Clark NM, KeteyianSR, Partridge M, Griffiths C. Educational and behavioral interventions for asthma: who achieves which outcomes? A systematic review. Journal of Asthma and Allergy. 2010: p.187.doi: 10.2147/jaa.s14772 . | Open in Read by QxMD
  5. Labre MP, Herman EJ, Dumitru GG, Valenzuela KA, Cechman CL. Public Health Interventions for Asthma. Am J Prev Med. 2012; 42 (4): p.403-410.doi: 10.1016/j.amepre.2011.11.016 . | Open in Read by QxMD
  6. Naar S, Ellis D, Cunningham P, et al. Comprehensive Community-Based Intervention and Asthma Outcomes in African American Adolescents. Pediatrics. 2018; 142 (4): p.e20173737.doi: 10.1542/peds.2017-3737 . | Open in Read by QxMD
  7. Trends in asthma prevalence, health care use, and mortality in the United States, 2001–2010. Updated: May 1, 2012. Accessed: April 30, 2019.
  8. Most Recent Asthma Data. Updated: February 27, 2017. Accessed: April 19, 2017.
  9. Gauvreau et al. Effects of Interleukin-13 Blockade on Allergen-induced Airway Responses in Mild Atopic Asthma. Am J Respir Crit Care Med. 2011; 183 (8): p.1007-1014.doi: 10.1164/rccm.201008-1210oc . | Open in Read by QxMD
  10. Lloyd CM, Hessel EM. Functions of T cells in asthma: more than just T(H)2 cells.. Nat Rev Immunol. 2010; 10 (12): p.838-48.doi: 10.1038/nri2870 . | Open in Read by QxMD
  11. Maselli DJ, Hardin M, Christenson SA, et al. Clinical Approach to the Therapy of Asthma-COPD Overlap. Chest. 2019; 155 (1): p.168-177.doi: 10.1016/j.chest.2018.07.028 . | Open in Read by QxMD
  12. Global Strategy for Asthma Management and Prevention (2022 update). Updated: January 1, 2022. Accessed: August 29, 2022.
  13. Global Initiative for Chronic Obstructive Lung Disease (GOLD). Global Strategy for the Diagnosis, Management, and Prevention of Chronic Obstructive Pulmonary Disease - 2023 Report. Updated: November 1, 2022. Accessed: November 30, 2022.
  14. Poylin V, Curran T, Cataldo T, Nagle D. Perioperative use of tamsulosin significantly decreases rates of urinary retention in men undergoing pelvic surgery. Int J Colorectal Dis. 2015; 30 (9): p.1223-1228.doi: 10.1007/s00384-015-2294-7 . | Open in Read by QxMD
  15. Sam A, Kraft M. Asthma-COPD Overlap. Curr Pulmonol Rep. 2022; 11 (1): p.1-14.doi: 10.1007/s13665-021-00284-0 . | Open in Read by QxMD
  16. Yang CL, Gaffin JM, Radhakrishnan D. Question 3: Can we diagnose asthma in children under the age of 5 years?. Paediatr Respir Rev. 2019; 29: p.25-30.doi: 10.1016/j.prrv.2018.10.003 . | Open in Read by QxMD
  17. Sakula A. Charcot-Leyden crystals and Curschmann spirals in asthmatic sputum. Thorax. 1986; 41 (7): p.503-7.
  18. Fahy JV, O'Byrne PM. "Reactive airways disease". A lazy term of uncertain meaning that should be abandoned.. Am J Respir Crit Care Med. 2001; 163 (4): p.822-3.doi: 10.1164/ajrccm.163.4.2005049 . | Open in Read by QxMD
  19. $ZYFLO® (zileuton tablets).
  20. $Intal® Nebulizer Solution (cromolyn sodium inhalation solution, USP).
  21. $XOLAIR® (omalizumab) for injection, for subcutaneous use.
  22. $NUCALA (mepolizumab) for injection, for subcutaneous use.
  23. Suissa S, Ernst P, Benayoun S, Baltzan M, Cai B. Low-Dose Inhaled Corticosteroids and the Prevention of Death from Asthma. N Engl J Med. 2000; 343 (5): p.332-336.doi: 10.1056/nejm200008033430504 . | Open in Read by QxMD
  24. Reddel HK, Ampon RD, Sawyer SM, Peters MJ. Risks associated with managing asthma without a preventer: urgent healthcare, poor asthma control and over-the-counter reliever use in a cross-sectional population survey. BMJ Open. 2017; 7 (9): p.e016688.doi: 10.1136/bmjopen-2017-016688 . | Open in Read by QxMD
  25. Suissa S. Regular use of inhaled corticosteroids and the long term prevention of hospitalisation for asthma. Thorax. 2002; 57 (10): p.880-884.doi: 10.1136/thorax.57.10.880 . | Open in Read by QxMD
  26. Agabegi SS, Agabegi ED. Step-Up To Medicine. Lippincott Williams & Wilkins ; 2013
  27. Le T, Bhushan V, Bagga HS. First Aid for the USMLE Step 2 CK. McGraw-Hill Medical ; 2009
  28. Fanta CH. Management of Acute Exacerbations of Asthma in Adults. In: Post TW, ed. UpToDate. Waltham, MA: UpToDate. Last updated: February 16, 2017. Accessed: April 19, 2017.
  29. Saadeh CK. Status Asthmaticus. In: Oppenheimer JJ, Status Asthmaticus. New York, NY: WebMD. Updated: March 3, 2017. Accessed: April 19, 2017.
  30. Little M. Asthma in Pregnancy. In: Pritchard Taylor J, Asthma in Pregnancy. New York, NY: WebMD. Updated: June 6, 2016. Accessed: April 19, 2017.
  31. Niimi A. Cough and asthma. Curr Respir Med Rev. 2011; 7 (1): p.47-54.doi: 10.2174/157339811794109327 . | Open in Read by QxMD
  32. David R Stather, Thomas E Stewart. Clinical review: mechanical ventilation in severe asthma. Crit Care. 2005; 9 (6): p.581-587.doi: 10.1186/cc3733 . | Open in Read by QxMD
  33. Fala L. Nucala (Mepolizumab): First IL-5 Antagonist Monoclonal Antibody FDA Approved for Maintenance Treatment of Patients with Severe Asthma.. American health & drug benefits. 2016; 9 (Spec Feature): p.106-10.
  34. Global Initiative for Asthma (GINA) GUIDE FOR ASTHMA MANAGEMENT AND PREVENTION. Updated: January 1, 2019. Accessed: May 1, 2019.
  35. Camargo CA, Rachelefsky G, Schatz M. Managing Asthma Exacerbations in the Emergency Department: Summary of the National Asthma Education and Prevention Program Expert Panel Report 3 Guidelines for the Management of Asthma Exacerbations. Proc Am Thorac Soc. 2009; 6 (4): p.357-366.doi: 10.1513/pats.p09st2 . | Open in Read by QxMD
  36. Brenner B, Corbridge T, Kazzi A. Intubation and Mechanical Ventilation of the Asthmatic Patient in Respiratory Failure. Proc Am Thorac Soc. 2009; 6 (4): p.371-379.doi: 10.1513/pats.p09st4 . | Open in Read by QxMD
  37. Prasad Kerlin M. Asthma. Ann Intern Med. 2014; 160 (5): p.ITC3-1.doi: 10.7326/0003-4819-160-5-201403040-01003 . | Open in Read by QxMD
  38. Dweik RA, Boggs PB, Erzurum SC, et al. An Official ATS Clinical Practice Guideline: Interpretation of Exhaled Nitric Oxide Levels (FeNO) for Clinical Applications. Am J Respir Crit Care Med. 2011; 184 (5): p.602-615.doi: 10.1164/rccm.9120-11st . | Open in Read by QxMD
  39. Pardue Jones B, Fleming GM, Otillio JK, Asokan I, Arnold DH. Pediatric acute asthma exacerbations: Evaluation and management from emergency department to intensive care unit. Journal of Asthma. 2016; 53 (6): p.607-617.doi: 10.3109/02770903.2015.1067323 . | Open in Read by QxMD
  40. Moriates C, Feldman L. Nebulized bronchodilators instead of metered-dose inhalers for obstructive pulmonary symptoms. Journal of Hospital Medicine. 2015; 10 (10): p.691-693.doi: 10.1002/jhm.2386 . | Open in Read by QxMD
  41. Simonds A, Hanak A, Chatwin M, et al. Evaluation of droplet dispersion during non-invasive ventilation, oxygen therapy, nebuliser treatment and chest physiotherapy in clinical practice: implications for management of pandemic influenza and other airborne infections. Health Technol Assess (Rockv). 2010; 14 (46): p.131-172.doi: 10.3310/hta14460-02 . | Open in Read by QxMD
  42. Dissanayake S, Suggett J. A review of the in vitro and in vivo valved holding chamber (VHC) literature with a focus on the AeroChamber Plus Flow-Vu Anti-static VHC. Therapeutic Advances in Respiratory Disease. 2018; 12: p.175346581775134.doi: 10.1177/1753465817751346 . | Open in Read by QxMD

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