Allergies may be described to the layperson as aversion against or hypersensitivity towards any particular object. These objects range from pollen grains and other polluting factors present in the air, to any kind of artificial flavoring in edible goods. The most prevalent and troublesome form of allergy is asthma, which is mainly related to the respiratory system.

Asthma is defined simply as reversible airway impediment. It is a chronic ailment that involves the respiratory system, within which the airway occasionally gets constricted, becomes irritated, and is lined with undue amounts of mucus, often in response to one or roots. These episodes may be triggered by things like exposure to an allergen such as cold, warm or moist air, perfume, exertion, or emotional pressure. Various are responsible for its manifestation. In children, the most common triggers are viral illnesses. The narrowing of the airway causes signs such as wheezing, short breath, tightness in the chest and coughing. Between attacks, most patients feel well but they may remain quite short of breath after exercise for longer periods of time than an unaffected individual. The symptoms of asthma, which range from mild to life threatening ones, can be controlled with a combination of medicines and environmental changes.

Asthma is caused by a composite interaction of genetic and environmental factors, and researchers have not fully understood them yet. These factors can also influence the severity of a person's asthma is and their response to medication. As with other multifaceted disorders, many factors have been recommended as causes of asthma, but not all of them have been acknowledged. Many environmental factors have been associated with the disease, but a few stand out as they have several studies to support their direct association. Many genes are also related to this disorder. However, even among the long list of highly replicated genes associated with asthma, the results have not been consistent. This indicates that these genes are not associated with asthma under every condition.

The most effective treatment for asthma is identifying the triggers that cause the disorder, and limiting or eradicating any kind of exposure to them. If trigger avoidance is inadequate, medical treatment is available. Desensitization is at present the only known "cure" to the disease. Current treatment protocols recommend prevention medications, which help to suppress any inflammation and reduce any swelling in the lining of the airways. If symptoms persist, additional precautionary drugs are added until the asthma is controlled. With the proper use of prevention drugs, can avoid the snags that result from the overuse of relief medications. Other kinds of treatment include prevention medication, relief medication, long-acting ?2-agonists, and emergency treatment.

Asthmatics sometimes stop taking their preventive medication when they begin to have no problems breathing. This frequently results in further attacks, and no long-term improvement.

Asthma prevalence, morbidity, mortality, and drug response vary greatly across different populations. The occurrence of asthma is highest among the low-income populations, which in the western world are ethnic minorities, and are more likely to live near industrial areas. In addition to this, asthma has been strongly associated with the presence of cockroaches in dwelling places, which is more likely in such neighborhoods.