Which of the following is a trigger for asthma?

Asthma triggers are diverse and can vary from person to person. Respiratory infections are a common trigger because they can cause inflammation and exacerbate asthma symptoms. When individuals with asthma catch a cold or flu, their airways may become more sensitive and reactive, leading to increased difficulty in breathing.

Exercise can also trigger asthma, especially in those who experience exercise-induced bronchoconstriction. During physical activities, the body may demand more oxygen, which can irritate the airways if they are already sensitive. This is particularly noticeable in cold, dry air, where people may notice symptoms like wheezing or shortness of breath during or after exercise.

Sudden changes in humidity or temperature can also act as triggers. For instance, a rapid shift from a very cold environment to a warm one, or from dry to humid conditions, can cause airway constriction. These changes can affect the respiratory system, leading to asthma symptoms.

Given that all these factors can provoke an asthma response, the comprehensive nature of the answer capturing all possible triggers demonstrates a clear understanding of the various elements that can impact individuals with asthma. Thus, identifying "All of the above" as the answer encompasses the broad range of potential triggers for asthma.