What is Asthma?
Asthma is a chronic inflammatory disease of the airways in the lungs characterised by bronchoconstriction (narrowing of the breathing tubes) and airway inflammation. Symptoms include coughing, wheezing, chest tightening and /or shortness of breath. There may also be exacerbations during which the airways fill with mucus. Asthma is an obstructive pulmonary disease, and these symptoms are the result of chronic airway inflammation [1]. Asthma is one of the most prevalent disorders in the world, affecting around 12% of the global population [2].
What are the Causes of Asthma?
Asthma has a multifactorial aetiology, with a wide range of factors being linked as potentially causing or contributing to it [3, 4]. Some factors are definitively linked to asthma in the following ways: having a family member with asthma is associated with a much higher risk of developing an asthmatic condition [3]; being exposed to allergens, industrial chemicals or smoke increases the risk of developing asthma; viral upper respiratory infections are linked to asthma onset; and asthma is commonly associated with eczema and allergic rhinitis (hay fever) [3].
Exposure to environmental factors such as dust, mold, pets, pollen, and pests, such as cockroaches or mice, commonly triggers asthma episodes in persons with asthma, as do non-allergic asthma triggers, including cold air, some medications, and household chemical irritants, as well as infections such as colds and flu, outdoor air pollution and tobacco smoke [4].
Allergic asthma is caused by an overreaction of the immune system to allergens, leading to inflammation of the airways. Common allergens include pollen, mold, dust mites, pet dander, and cockroach droppings [5]. Non-allergic asthma is triggered by factors that are not allergens, such as cold air, certain medicines, household chemicals, infections, outdoor air pollution, and tobacco smoke [4].
Other risk factors include obesity, certain lung infections, preterm birth and environmental triggers [6]. However being exposed to any of these risk factors does not guarantee that you will develop asthma, just as negative triggers are not universal but differ among individuals.
Risk Factors of Asthma
Asthma is a chronic disease that affects the airways, causing inflammation and narrowing. The exact causes of asthma are not known, but several risk factors have been identified.
Perhaps the most important risk factor is heredity. Having one parent with asthma puts you at 3-6 times increased risk compared with those whose parents have not got asthma [3].
Exposure to allergens, including dust mites, pet dander, mold spores, pollen and certain foods, can also raise the risk of developing asthma [3].
Environmental factors are also important factors: exposure to air pollution, second-hand smoke and some chemicals or gases are linked to the development of asthma [3, 7].
Many health conditions, including obesity and problems with the skin, such as allergies, eczema and hay fever, also appear to aggravate the risk of asthma [3].
Risk factors for children are prematurity, birth weight, and respiratory infections [3, 7]; for children, it is more prevalent in boys, but for adults, it is more prevalent in women [3].
Race and ethnicity are also factors, with asthma at markedly higher rates in Black, Hispanic, Native American and Alaska Native communities [3].
Lastly, exposure to chronic stress or adversity, such as poverty or family conflict, can increase the risk of asthma [7].
What is COVID-19?
COVID-19, short for Coronavirus Disease 2019, is an infectious disease caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) [8, 9, 10, 11, 12, 13, 14, 15]. This virus is part of the larger coronavirus family, which can cause diseases in a variety of species, including humans [8, 9, 13, 15].
Causes of COVID-19
COVID-19 is primarily a respiratory disease, yet other organs can also be affected [14]. The virus transmits via the release of droplets and minute airborne particles from an infected individual when they breathe out [12]. It’s a respiratory disease, transmitted by exposure to a person singly and aerosolised particles containing a virus when they cough or sneeze [10].
Here the virus attacks the lower airways and can cause severe acute respiratory syndrome (SARS) [11]. Worse outcomes could result in secondary complications such as acute respiratory distress syndrome, acute kidney disease, liver damage and even multi-organ dysfunction and fatality [15].
Can COVID-19 Cause Asthma?
The correlation between COVID-19 and asthma is not clear-cut, but there are some reports of people who had been sick with COVID-19 and new-onset asthma-like symptoms were reported following recovery from the original infection.
For example, one small human case series published in 2021 showed that many people without allergies or asthma reported having an asthma-like syndrome about 1-6 months following recovery from COVID-19 [16]. Another study from human case reports of paediatric patients admitted to hospital with COVID-19 identified asthma-like symptoms following recovery from COVID-19 as the cause for about 41.5% of those hospitalised with COVID-19 [16].
Nevertheless, these findings certainly do not prove that COVID-19 is a cause of asthma. Rather, the symptoms being described could be due to long-term damage to the airways in the lungs, caused by the effects of COVID-19 infection, which are contributing to breathing difficulties, similar to those experienced by people with asthma [16].
Conversely, previous asthma doesn’t appear to raise the risk for severe COVID-19. It seems that those with asthma have no heightened risk of infection with SARS-CoV-2 or more severe disease if infected with COVID-19 [17]. Some studies suggest that people with asthma could have a higher risk of long COVID, and have worse experience of asthma symptoms [16].
Conclusion
Overall, there is some indirect evidence that asthma-like symptoms can develop after COVID-19, but there are currently no strong study designs to measure an association between COVID-19 infection and asthma. More research is needed to definitively know whether COVID-19 can lead to the onset of asthma.