Asthma is a chronic inflammatory respiratory disease that manifests itself in repeated obstruction of the airways. The chronic inflammation is a result of heightened sensitivity to certain trigger substances, which leads to airways obstruction due to greater production of mucus and increased contraction of the smooth muscles in the bronchus (bronchospasm). Asthma is a heterogeneous disease with various different aetiologies, triggers, signs and symptoms and responses to treatment. It’s an important health problem, as it’s the most frequent type of chronic lung diseases, affecting around 400 million people around the globe. The number of asthmatic patients is increasing, especially in the countries with low-to-moderate income.

Long-term control of asthmatic symptoms involves lowering the inflammatory response by avoiding environmental triggers, taking anti-inflammatory drugs and managing associated conditions that may make asthma worse.

Causes

The exact cause for asthma isn’t entirely known. Research attributes it to a combination of environmental factors and the genetic predisposition of an individual. It’s assumed that asthma appearing before the age of 12 is due more to genetic factors, while environmental factors play a greater role in asthma that appears later in life.

Asthma is also closely connected to allergic rhinitis. Allergic rhinitis affects as much as 20-30% of the world population, and asthma develops in nearly half of the patients. The appropriate treatment of allergic rhinitis is an important step in preventing asthma, nasal polyps and the loss of smell.

Genetics

Asthma develops more frequently in individuals with family history of the illness. There are a number of genes responsible for asthma, most of them connected to the development of the immune system, the synthesis of cytokines (proteins secreted by certain immune cells during an immune response) and the regulation of other inflammatory mechanisms. The expression of these genes is likewise influenced by the environment and the age at which one is exposed to environmental factors as a child.

Environment

It’s proven that smoking during pregnancy and after birth increases the risk of asthma in the child. Other risk factors include virus infections (especially those causing pneumonia or bronchiolitis: rhinoviruses, RSV, influenza virus, parainfluenza virus and adenovirus) in early childhood, air pollution, atopy and the sensitization to food or inhaled allergens.

Cold and dry air, strong smells and quickened breathing due to physical exercise don’t cause asthma but only trigger bronchospasms in people who already have the illness. These triggers worsen the inflammation in the affected individual, which leads to increased production of mucus and, at the same time, increases bronchospasms.

Pathogenesis

In smaller airways, the airflow is regulated by smooth muscles that surround the lumen of the airways. During an asthmatic episode, the airways become inflamed due to environmental triggers, which leads to the contraction of smooth muscles and thus to the direct and, in some cases, even a complete closure of the airflow. Aside from bronchoconstriction, the already constricted airways can be further blocked by increased secretion of mucus, which triggers coughing and other breathing difficulties. Due to the chronic course of asthma, patients typically have damaged epithelium, thickened basement membrane (with typical eosinophilic infiltration) and hypertrophy of smooth muscles. The inflammatory process maintains the levels of helper T cells and other immune cells that produce anti-inflammatory cytokines . Bronchospasms can resolve spontane (IL-4, IL-5, IL-13)ously or through therapy. However, in 50% of cases, they become a part of a late response that follows the first one after 3 to 12 hours and takes the form of repeated bronchoconstriction and inflammation.