Causes of asthma

Asthma can be due to inheritance, environment or lifestyle or, which is likely, a combination of several factors.

Both twin studies and the mapping of the genetic code in people with and without asthma show that the disease is largely hereditary.

Environment and lifestyle affect the risk of getting asthma
In addition to hereditary factors, the modern man’s environment and lifestyle are believed to be an important explanation for why more and more children have asthma. Changes in the way of life and in the indoor environment are considered to be possible contributing causes, as well as changes in diet and increased body weight.

Factors in the environment are important for respiratory symptoms. Smoking in the home, poor ventilation, moisture and mold are often related to asthmatic problems, as well as severe outdoor air pollution. Various occupational exposures can also cause asthma.

New research also shows that the gut flora is important for the development of asthma as well as that premature babies have an increased risk of impaired lung function with asthma-like symptoms.

One factor that is usually mentioned is the hygiene hypothesis. According to the hypothesis, the fact that the hygiene standard in our part of the world is so high would have led to an underestimation of the immune system, which explains that the prevalence of asthma has increased in recent decades, especially in children.

Allergens and irritants
We all carry antibodies whose task is to form a defense against substances that are foreign to the body. Allergists have a “malfunctioning” in their defense that causes special antibodies to react to natural substances in the environment that are not dangerous. These substances are called allergens. In Sweden, the most common allergens come from cat, dog, birch and grass pollen.

The first time a person with a hereditary tendency to develop allergies comes into contact with or inhales an allergen is formed so-called IgE antibodies. Upon the next inhalation or contact with the allergen, the IgE antibodies recognize the foreign substance – which they perceive as dangerous – and react.

Asthma attacks can be triggered by allergens, but also by so-called irritants found in the environment. These are substances that irritate the trachea such as tobacco smoke, car exhaust and strong odors. Exercise and cold can also contribute to an asthma attack. People who only respond to irritants have a so-called non-allergic asthma. Even for people with allergic asthma, the irritants can trigger an asthma attack.

Asthma can debut at any age
Asthma can occur at any time during life, although it is most common for the disease to debut in childhood. Asthma patients can also be divided into three groups based on age of onset.

The first group gets asthma as very small and it is often caused by an airway infection, for example by the RS virus. These children tend to also later suffer from asthma in respiratory tract infections. The group is dominated by boys. The risk of asthma increases if the mother smokes during pregnancy and if one of the parents continues to smoke when the baby is born. This type of asthma can “grow away” as the children’s trachea continues, the infections come at longer intervals and the mucous membranes heal.

The second group consists of people with an allergic disease where most have developed asthma before or during the school years. However, the development varies and this type of asthma can debut even in adulthood.

In the third group, asthma debuted in adulthood. Most often these are non-allergic asthma that occurs in connection with an infection. This type of asthma is more common in smokers, overweight and women.

Between 10 and 15 percent of all new cases of adult asthma are likely due to exposure to allergenic substances in the workplace.

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