Asthma is a chronic lung disease that causes difficulty breathing due to inflammation and narrowing of the airways. Asthma symptoms include wheezing, coughing, chest tightness and shortness of breath. Asthma is quite common, affecting around 25 million people in the United States. While asthma can develop at any age, it most often begins in childhood. This leads many to wonder – are you born with asthma or do you develop it later in life? The short answer is that both factors play a role. There is a genetic component to developing asthma, but environmental triggers also substantially influence whether someone will ultimately have asthma.
Genetic Factors
Genetics account for around 60% of the risk of developing asthma, so there is definitely a hereditary element. Children born to parents who both have asthma are significantly more likely to develop asthma themselves compared to the general population. The odds increase if the mother has asthma versus just the father having it. Identical twins are also more likely to both have asthma compared to fraternal twins. Additionally, those with certain genetic variants passed down are at higher risk of asthma. Some variants linked to increased asthma risk affect immune functioning or airway reactivity and inflammation. So in a sense, a genetic predisposition for asthma is present at birth for some individuals. However, this genetic risk alone is not enough for most people to develop asthma. Environmental triggers are still needed to bring about asthma symptoms in those with a genetic vulnerability.
Environmental Triggers
While genetics load the gun, so to speak, certain environmental exposures and conditions pull the trigger for asthma to develop. The most common asthma triggers include:
- Allergens – Such as pollen, pet dander, dust mites, mold
- Irritants – Such as cigarette smoke, air pollution, chemicals/strong odors
- Respiratory Infections – Especially in early childhood
- Exercise – For some people, vigorous activity can trigger asthma symptoms
- Weather Changes – Cold air, changes in humidity and barometric pressure
- Medications – Including aspirin and other NSAIDs
- Gastroesophageal Reflux Disease (GERD)
- Obesity
Exposure to these triggers prompts an immune reaction that leads to airway inflammation and asthma symptoms in those with a genetic vulnerability. The timing of exposure to these environmental factors, especially early in life, impacts whether asthma ultimately develops.
Early Life Exposures
Exposures early in life, even in utero, can set the stage for eventual asthma development. These include:
- Maternal smoking during pregnancy
- Low birth weight
- Exposure to air pollution/tobacco smoke as an infant
- Respiratory viral infections in early childhood
- Microbial exposures and gut bacteria imbalances
Altered immune functioning early in development may promote tendencies for inflammation and allergies. Having certain infections like RSV as a baby also seem to kickstart immune and inflammatory changes that increase asthma risk. However, a “hygiene hypothesis” suggests that reduced microbial exposures in modern life may also boost risks of immune hypersensitivities. Overall, various early exposures can tune the immune system to be primed for asthma development when later triggers are encountered.
Peak Ages of Onset
Given the impact of early childhood exposures, it’s not surprising that asthma most often develops in the first few years of life. However, a second peak occurs during the teenage adolescent growth spurt. The typical ages when asthma starts are:
- Before age 5 (early childhood asthma)
- Around puberty (10-17 years old)
- In adulthood (occupational asthma)
Younger children have smaller, developing airways that are more prone to inflammation and narrowing. But for teenagers, hormonal shifts and growth spurts likely contribute to new asthma onset. Occupational exposures are a common cause of new asthma cases in adulthood as well. Overall, the timing of various environmental exposures interacts with genetic risk to influence when asthma emerges.
Is Asthma Reversible?
For children who develop asthma, around half will outgrow their asthma by the time they are adults. However, some asthma beginning in childhood can persist throughout the rest of life. Once asthma develops, it is a chronic condition. But keeping asthma under good control with medication and avoiding triggers can help minimize flare-ups long-term. For some adults, occupational asthma may improve once the exposures triggering it are removed. But in most other cases, asthma is managed rather than cured once present. The sensitive airways and immune tendencies programmed early in life can make asthma symptoms an ongoing intermittently challenge.
Risk Factors Over Time
To summarize, the development of asthma involves genetic risks mixing with changing environmental exposures from the womb through childhood and beyond:
| Time Period | Risk Factors |
|---|---|
| In utero | Maternal smoking, maternal asthma, low birth weight |
| Infancy | Tobacco smoke, air pollution, respiratory infections |
| Early childhood | Allergen exposures, more respiratory infections |
| School age | Allergies, exercise, weather changes |
| Adolescence | Hormonal changes, growth spurts |
| Adulthood | Occupational irritants, obesity, medications |
Conclusion
In summary, asthma arises from an interaction between inborn genetic risks and various environmental exposures throughout life. While some inherit a predisposition for sensitive airways, actual onset of asthma still depends on encountering triggers that provoke airway inflammation. The timing and type of these triggers determines when and if asthma symptoms emerge, especially early in life. Asthma is complex disease with both hereditary and environmental components contributing to its development. For some individuals, reducing exposures to environmental triggers may help reduce symptoms long-term. But for most, asthma becomes an ongoing disease requiring chronic management once it develops. Through better understanding the various factors underlying asthma, we can improve prevention efforts as well as treatments.