What are the causes of asthma?

From the Guidelines

Asthma is caused by a combination of genetic and environmental factors that lead to chronic inflammation and hyperresponsiveness of the airways, with the most significant factors being airborne allergens, viral respiratory infections, and genetic predisposition. The development of asthma involves the interplay between host factors, particularly genetics, and environmental exposures that occur at a crucial time in the development of the immune system 1. People with a family history of asthma or allergies have a higher risk of developing the condition. Environmental triggers play a significant role, including allergens (dust mites, pollen, pet dander), respiratory infections, air pollutants, tobacco smoke, and certain medications like aspirin or beta-blockers.

When exposed to these triggers, the airways of asthmatic individuals become inflamed, the surrounding muscles tighten, and excess mucus is produced, causing narrowing of the airways and difficulty breathing. Some key points to consider include:

• Airborne allergens, such as house dust mite and Alternaria, are major factors in the development and persistence of asthma 1
• Viral respiratory infections, including respiratory syncytial virus and rhinovirus, can trigger asthma exacerbations and may contribute to the development of asthma 1
• Genetic factors, including the linkage of genetic factors to different asthma phenotypes, can influence the development and severity of asthma 1
• Occupational exposures to chemicals, dust, or fumes can also cause asthma in some individuals 1
• Additionally, obesity, stress, and hormonal changes may contribute to asthma development or worsen existing symptoms.

The underlying mechanism involves an abnormal immune response where the body overreacts to certain substances, releasing chemicals that cause inflammation and bronchospasm. While asthma cannot be cured, it can be effectively managed with proper medication, trigger avoidance, and regular medical follow-up. According to the expert panel report 3 (EPR-3) guidelines for the diagnosis and management of asthma, the working definition of asthma is a chronic inflammatory disorder of the airways in which many cells and cellular elements play a role 1.

From the Research

Causes of Asthma

The causes of asthma are complex and multifaceted. Some of the key factors that contribute to the development of asthma include:

• Genetic predisposition 2, 3, 4
• Environmental exposure to inhaled substances and particles that may provoke allergic reactions or irritate the airways, such as:
  • In- and out-door allergens 2, 3
  • Tobacco smoke 2, 3
  • Chemical irritants in the workplace 2
  • Air pollution 2, 4
• Infections, which can trigger and promote disease progression 2, 5
• Abnormal or inadequately regulated CD4+ T-cell immune response, leading to an overactive T-helper 2 (Th2) subset and dampened Th1 activity 3
• Epigenetic changes, which can be influenced by environmental factors such as smoking and traffic pollution 4

Pathophysiology of Asthma

The underlying pathophysiology of asthma is airway inflammation, which is characterized by:

• Increased mucus production 5, 3
• Airway hyper-responsiveness 5, 3
• Bronchial airway inflammation resulting in airflow limitation 3
• Multicellular inflammatory pattern, with mast cells, neutrophils, eosinophils, T lymphocytes, and epithelial cells participating in the response 5