Immune System
Asthma is the result of an overactive immune system. Although doctors don't totally understand what causes asthma, the unusual activity of the immune system is thought to have a genetic component. In asthmatics, a specific part of the immune system, called the humoral immune system, is very sensitive. The humoral immune system typically deals with the early response to pathogens, and in some cases it can be set off by allergies. However, in some asthmatics, an asthma attack can be triggered by other things that either irritate the airways or activate the immune system.
Asthma Triggers
An asthma attack is brought on by the patient being exposed to a "trigger," which is a stimulus that activates the immune system. The most common trigger is some type of allergen, such as dust, smoke or pollen. In an asthmatic, these allergens cause a massive immune reaction, which leads to inflammation of the airways. However, there are triggers aside from allergens. Some asthmatics can have an asthma attack in response to cold air or exercise. Others can have their asthma triggered by the irritation from heartburn. Stress can also lead to an asthma attack, as can some medications or changes in the menstrual cycle.
Effects
Regardless of the trigger, asthma symptoms are marked by the inflammation that results from the immune system becoming abnormally activated. One result of inflammation around the airways is swelling, which can cause the airways becoming closed off. Inflammation also causes the smooth muscles around the airways to constrict (also known as bronchospasm), which can also narrow the airways, making it difficult to breathe, sometimes causing wheezing. Inflammation also causes cells in the airways to secrete mucus. This mucus eventually trickles into the lungs and causes coughing.
