Many studies have confirmed that allergies cause the greatest majority of childhood asthma cases. Doctors refer to cases of asthma that are caused by allergies as atopic asthma. Atopic asthma is the most common form of asthma and tends to run in families. It is an inherited over reaction—hypersensitivity—to allergens in the environment and the related overproduction of IgE antibodies by the human immune system. Antibodies produced by the immune system combine with allergens. This action stimulates an asthma attack, in which the immune system releases substances that bring on the constriction and inflammation of the airways of the lungs.

More than 80% of asthmatic patients also suffer from allergies such as hay fever. The medical term for hay fever is allergic rhinitis. Allergic rhinitis is the most common cause of atopic asthma. Many types of allergens can trigger the immune system to produce the typical hay fever symptoms that mainly affect the nasal region, such as stuffiness and a runny nose. The term "hay fever" does not accurately describe this problem, because it is rarely caused by hay and does not produce a fever in affected patients. Allergies even aggravate asthma in patients whose asthma was not originally caused by allergic factors. Small amounts of inhaled or swallowed allergens do not directly harm the tissues of the airways and lungs. However, they unfortunately act as triggers that set off the chain of events in the immune system that produce the symptoms typical of asthma.

People with asthma have increased sensitivity to allergens in the air they breathe in. Allergies are the human immune system's reaction to biological triggers—including indoor allergens such as dust mites, animal dander (pet hair or feathers), saliva, flakes of skin, secretions from pets and insects, mold, and substances found in food. Even "hairless" dogs can be a problem for asthmatic patients. Some foods, such as peanut, dairy products, and seafood, can cause attacks in some asthmatic children. Food additives, such as sulfites, and even natural foods like eggs, shellfish, and raw vegetables can act as triggers for asthma. Endotoxins, which are chemicals produced by molds growing on farm products, may contribute to asthma in agricultural areas. Synthetic (man-made) products like the latex material used in surgical gloves can also trigger asthma episodes.

In some of the more "developed" countries, an important contributing factor in the growing number of atopic asthma cases may be the reduced exposure to common childhood respiratory infections such as the flu and colds. Recent studies have shown that children who live in very clean, hygienic conditions and are relatively isolated from other young people are more likely to develop asthma later in life. This is commonly referred to as the "hygiene theory." It seems that children with older siblings and who attend day care programs where they may contract such illnesses have a lower risk for developing asthma. A possible explanation for this seemingly strange connection is that a child's immune system is fine tuned, or conditioned, by contact with these infectious organisms and other foreign agents at a very young age.

Non-Allergic Factors:

Non-allergic factors that can stimulate or aggravate asthma symptoms include tobacco smoke, chalk dust and talcum powder, cooking fumes, and fumes from chemicals such as household cleaners. Certain behaviors such as stress and emotional anxiety can also trigger asthmatic attacks. Young children can develop asthma or cause asthmatic episodes as a result of viral infections such as colds, flu, and pneumonia.

Exercise is a common trigger for asthma in about 80% of asthmatic individuals. In some asthmatic patients, exercise induces typical asthma symptoms such as coughing, wheezing, and shortness of breath. Symptoms may appear during or after participation in physical activity. Pretreatment medications, such as short-acting bronchiodilators, quickly widen the air passages and thus help prevent the onset of asthma while a patient participates in physical activities. Some doctors advise their asthmatic patients to participate in sports like baseball or football that provide frequent breaks in activity rather than prolonged endurance sports such as swimming and long distance running.

Asthma does not have to be a barrier to participating in athletic activities. For example, 67 of the 596 members of the United States team at the 1984 Olympics tested positive for exercise-induced asthma, and that team won 41 Olympic medals. In addition, another survey revealed that 50% of the athletes participating in the 1996 Olympics displayed some form of asthmatic symptoms.

Changes in the weather, such as temperature and humidity variations can also negatively affect asthma patients. Winter is a tough time for people with asthma. They have difficulty in conditioning—warming up and humidifying—the air they breathe in. Some people with asthma wear a surgical mask that can trap warm, moist air that is exhaled with each breath. During cold weather, these individuals tend to spend more time indoors where they are more likely to catch contagious viral infections. Viral infections of the respiratory system are more likely to trigger severe asthmatic attacks during the winter months. In addition, unclean and poorly maintained forced air heating systems release many pollutants that further aggravate asthmatic symptoms.