Asthma is a common condition, but the causes are not well understood. Many things can contribute to someone developing asthma, and many triggers can lead to a flare-up or asthma attack. Some causes of asthma are unavoidable, while others are somewhat avoidable. Knowing the cause of asthma can help avoid potential triggers and guide treatment.


One factor that plays a role in asthma is genetics. Asthma is a complex disease with many components, but research shows that it does run in families and genetics play a role. Researchers believe that it follows an autosomal recessive inheritance pattern, meaning that two copies of a gene carrying asthma must be present. In other words, two people who have asthma are very likely to pass it to their offspring.



Another cause of asthma is allergies. While allergens can trigger an asthma attack, the relationship between cause and effect may be more complex. Some people with asthma also have other allergic conditions. It is commonly part of a series of reactions following a pattern that begins with eczema then leads to the development of food allergies, hay fever, and asthma, in that order.


Respiratory Infections

Respiratory infections are another of the common causes of asthma, especially in childhood. Studies show that increased asthma symptoms are associated with viral infections. In one study, 80 percent of flares in children with asthma resulted from viral infections, with rhinovirus causing 61 percent of them.

Although RSV only accounted for 5 percent of episodes in the study, it is a potent cause of wheezing in infants and can be quite serious.



Environmental factors are also a potent asthma cause. There are many ways that allergens and pollutants can affect the airway. They could act as a trigger, causing an asthma attack in someone already diagnosed with asthma. Or, a pollutant could irritate the airway and cause lingering hyper-responsiveness after the exposure ends.

Allergens and pollutants may also change the body's immune response, intensifying its reaction to future exposure.


Autonomic Imbalance

Studies into asthma causes indicate an autonomic imbalance may lead to asthma. The airway is innervated with autonomic nerves that control the function of the internal organs. Studies suggest that the brain's mechanism for controlling the autonomic nervous system may be abnormal in some people with asthma, leading to throat constriction and increased production of secretions in the airways.



Another of the known asthma causes is aspirin. Asthma is an aspirin-exacerbated respiratory disease, along with recurring nasal polyps and sensitivity to aspirin and other NSAIDs.

Aspirin-induced asthma typically begins when a person reaches their 30s or 40s and can come on quickly. Symptoms include asthma flares, coughing, wheezing, sneezing, and nasal congestion. The cause is unknown, but researchers believe it is not inherited and does not result from an allergic reaction.



Exercise is another common asthma cause. Exercise-induced asthma occurs when the airways constrict or get smaller during physical activity. It is triggered by any sport or exercise, and symptoms can persist even after the activity stops. These symptoms are worse when pollutants or irritants are also present or when the air is dry or cold.

This form of asthma is extremely common, and about 10 percent of cases occur in people who have not been previously diagnosed with asthma.


Eosinophilic Asthma

Eosinophilic asthma is a subtype of asthma that commonly develops in adulthood but can occur in children and teens. It is different from other causes of asthma as it involves eosinophils, a type of white blood cell.

In this type of asthma, eosinophils increase in the blood, lungs, and mucous — a reaction that affects the entire airway, from the sinuses to the lungs. Eosinophilic asthma ranges in severity, and the higher the number of eosinophils in the blood, the more risk there is for a severe asthma attack in the future.


Nocturnal Asthma

Nocturnal asthma is not necessarily one of the unique asthma causes, but it does affect some people who have asthma and has its own triggers.

Nocturnal or nighttime asthma is when asthma is worse at night. Doctors believe that it is caused by many things, including sleeping position, breathing in cooler air at night, experiencing increased exposure to allergens like dust at night, hormonal changes, or poor control of daytime symptoms.



One of the most serious health concerns, in general, is obesity, and it seems to be connected to asthma. Not only are people with obesity more likely to develop asthma, but they are also more likely to have worse symptoms and poorer control over them.

Obesity affects lung volume and blood flow, and it can even alter how well someone responds to their asthma medication. Research also shows that losing weight often leads to an improvement in asthma symptoms.


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