A Closer Look at Asthma: The Most Important Questions and Scientific Answers for Patients

This article is based on the comprehensive review “Asthma epidemiology and risk factors,” published in Seminars in Immunopathology (Volume 42, pages 21–40) in 2020 by Dr. Jessica Stern, Dr. Jennifer Pier, and Dr. Augusto A. Litonjua from the University of Rochester, USA. The authors are leading experts and researchers in the fields of allergy, immunology, and pulmonary medicine, with extensive clinical and academic experience in the study and treatment of asthma.

In the following sections, you will find answers to key questions that concern patients and their loved ones—curated and explained solely based on the scientific information from the referenced publication. Each question and answer is presented in a way that aims to deliver the most practical and evidence-based knowledge about asthma, its manifestations, and its social implications.

“Asthma is the most common chronic disease of childhood, affecting more than 300 million people worldwide. It results from a complex interaction between genes, the immune system, and the environment.”

Expert Insights

Asthma is one of the most widespread chronic diseases globally, affecting over 300 million people. It is not simply an “allergy” or a “childhood issue”—asthma is a complex clinical syndrome that encompasses a wide variety of causes, symptoms, and risk factors. Over the past few decades, its prevalence has been increasing, especially in developing countries. While some developed nations have seen a stabilization or slight decline, asthma remains a significant public health and socioeconomic concern.

Patients, their families, and even healthcare professionals often encounter conflicting advice and uncertainties: What causes asthma? What do we now know about the role of vitamin D, pollution, the microbiome, or stress? Is there a genetic predisposition, and can we make changes in our daily lives to reduce our risk?

The expert insights below present the latest scientific perspectives on the epidemiology, causes, and risk factors involved in the development and worsening of asthma. Each section begins with a guiding question or headline to help patients and their families navigate the most current and debated topics.

1. What is asthma and how is it diagnosed?

“The National Asthma Education and Prevention Program Expert Panel Report 3 (NAEPP3) defines asthma as ‘a chronic inflammatory disorder of the airways in which many cells and cellular elements play a role: in particular, mast cells, eosinophils, neutrophils (especially in sudden onset, fatal exacerbations, occupational asthma, and patients who smoke), T lymphocytes, macrophages, and epithelial cells. In susceptible individuals, this inflammation causes recurrent episodes of coughing (particularly at night or early in the morning), wheezing, breathlessness, and chest tightness. These episodes are usually associated with widespread but variable airflow obstruction that is often reversible either spontaneously or with treatment.’”

Explanation: Asthma is a chronic inflammatory disease of the airways that presents with episodes of coughing, wheezing, shortness of breath, and chest tightness. Importantly, there is no single “gold standard” for diagnosis; physicians rely on a combination of symptoms, family history, and functional tests like spirometry.

2. What are the main risk factors for developing or worsening asthma? (Vitamin D and the immune system)

“Over the last decade, there has been increasing interest in the role of vitamin D in asthma. There have been many studies which have suggested that deficiency in vitamin D may play a role in the severity of symptoms. Vitamin D and activation of the vitamin D receptor has been shown to have immunomodulatory and anti-inflammatory properties. … In combined analysis of two randomized controlled trials in humans, it was shown that prenatal vitamin D supplementation resulted in a reduced risk of asthma at 3 years of age in the offspring.”

Explanation: Vitamin D deficiency is linked to poorer asthma control, more severe symptoms, and more frequent exacerbations. Of particular interest is the impact of vitamin D supplementation during pregnancy—some studies have shown it may reduce the risk of asthma in children. While the exact mechanisms and recommended doses are still under investigation, the connection between immunity and vitamin D is well established.

3. What role does the microbiome and early microbial exposure play in asthma development?

“Many epidemiological studies have shown that exposure to diverse environmental microorganisms, especially early in life, can help to limit atopic disease. … It is now well studied that European children with early farm exposure have lower rates of asthma, likely due to the increased exposure to diverse microorganisms.”

Explanation: Children who grow up in rural areas, around animals and diverse microbes, are at lower risk of developing asthma. Controlled microbial exposure early in life teaches the immune system not to overreact to otherwise harmless substances such as allergens. This also explains why children raised with pets or multiple siblings tend to have lower rates of allergic conditions.

4. Environmental impact: Air pollution and tobacco smoke

“Urbanization and the resulting air pollution have been attributed to asthma exacerbations, as well as the development of asthma. One study in Europe found that 14% of pediatric asthma cases and 15% of all pediatric asthma exacerbations could be attributed to air pollution. … Both active and passive tobacco smoke exposures resulted in high rates of adult-onset wheezing and asthma.”

Explanation: Air pollution—especially fine particulate matter, nitrogen oxides, and ozone—as well as tobacco smoke (both firsthand and secondhand), are among the strongest proven risk factors for triggering and worsening asthma. Exposure during pregnancy and early childhood is particularly harmful, as it affects lung development. In some regions, efforts to reduce air pollution have led to noticeable declines in asthma incidence and exacerbations.

5. Genetic factors: What role does heredity play in asthma?

“While environmental factors play a big role in the development of asthma, genetic factors have been shown to contribute. Studies that have investigated the genetic heritability (the degree of variability in the phenotype in a population that is due to the genetic variation among individuals in that population) of asthma have shown estimates of 35 to 95%. … One of the most studied loci in asthma genetics is the 17q21 locus and contains several genes, most importantly ORMDL3 and GSDMB. This locus was initially identified through GWAS and has been replicated many times, particularly in childhood asthma.”

Explanation: Asthma is a multifactorial disease that often runs in families with histories of respiratory or allergic conditions. Recent genetic research has identified dozens of genes associated with asthma susceptibility. This helps explain why some individuals are more vulnerable, even under similar environmental conditions. In the future, genetic information may enable more precise, personalized approaches to prevention and treatment.

Q&A

1. Do age, gender, or ethnicity affect how asthma presents or progresses?

Answer: Yes, there are significant differences. Asthma is more common in boys during childhood, but in adulthood, it is more prevalent in women—suggesting a possible role of sex hormones. Additionally, the prevalence and severity of asthma vary across ethnic and socioeconomic groups. For example, in the U.S., asthma rates are highest among Puerto Rican (12.8%) and African American (10.1%) children, while Mexican American children have lower rates (5.1%). Poverty is also associated with higher prevalence and greater disease severity.

2. What are the most common conditions that are mistaken for asthma?

Answer: Asthma symptoms such as wheezing, coughing, and shortness of breath can also occur in other conditions—including viral or bacterial respiratory infections (e.g., bronchiolitis, tracheitis), structural abnormalities of the airways (e.g., stenosis, fistulas), foreign body aspiration, cystic fibrosis, gastroesophageal reflux disease, allergic or non-allergic rhinitis, and even vocal cord dysfunction. In adults, asthma is often confused with chronic obstructive pulmonary disease (COPD) or less common conditions like sarcoidosis or hypersensitivity pneumonitis.

3. How does asthma affect daily life, and what are the economic impacts?

Answer: Asthma carries a significant health and social burden. In the U.S., the total annual costs—including medical care, missed work and school days, and premature mortality—were estimated at $56 billion as of 2007 (adjusted for that year’s prices). The disease leads to millions of doctor visits, hundreds of thousands of hospitalizations, and frequent school and work absences. People with lower incomes are disproportionately affected, resulting in notable financial losses for individuals and society.

4. What role do allergens play, and which are the most common ones that worsen asthma?

Answer: Allergen exposure is a leading trigger for both the onset and exacerbation of asthma. The most common allergens include dust mites, cat and dog dander, molds, cockroach and rodent allergens. Many children with asthma are sensitized to at least one indoor allergen, and frequent exposure can lead to more frequent and severe asthma attacks. Avoiding allergens—when possible—is an important part of asthma management, though it’s not always feasible, especially in the case of pets or environmental allergens.

5. Why are some populations more frequently and severely affected by asthma? What are the social aspects?

Answer: There are marked disparities in asthma prevalence and outcomes that stem not only from genetics but also from socioeconomic, environmental, and healthcare access factors. In the U.S., for example, Black and Latino children are more likely to experience severe asthma, be hospitalized, and have higher mortality rates. These disparities are driven by a combination of limited access to quality healthcare, poor housing conditions, greater exposure to allergens and pollutants, and social stressors such as discrimination. Genetics and geography alone cannot fully explain these differences—poverty and social injustice play a crucial role.

Conclusion

Asthma is a multifaceted condition shaped by biological, environmental, and social factors that influence both risk and disease severity. The data and analysis presented by Dr. Stern, Dr. Pier, and Dr. Litonjua underscore the need for an individualized approach to each patient—taking into account age, ethnicity, social environment, and coexisting conditions. Understanding the complex picture of asthma’s causes and manifestations enables patients, families, and healthcare professionals to make more informed decisions about prevention and treatment. It also highlights the importance of social justice, healthcare access, and environmental quality in managing the disease effectively.

Source: Stern, J., Pier, J., & Litonjua, A. A. (2020). Asthma epidemiology and risk factors. Seminars in Immunopathology, 42, 21–40. https://doi.org/10.1007/s00281-020-00785-1