My child's asthma symptoms come and go. Why?

Yes... Asthma, by definition, consists of recurrent episodes of bronchospasm and airway inflammation. These episodes can be triggered by allergies, upper respiratory infections, etc. Between episodes, most patients are entirely normal. Patients should avoid known allergic triggers as much as possible. Patients with acute symptoms like wheezing, cough, shortness of breath need emergent eval, even er.
Triggers. Some things make asthma symptoms worse. These are called triggers, because they “trigger” symptoms. Common triggers are animal fur, pollen, mold, dust, cigarette smoke. Cold and flu can also trigger asthma symptoms. Staying away from or getting rid of the triggers will help.