Participants will be followed prospectively for the onset of a cold and a subsequent asthma exacerbation. An internet-based asthma and cold symptom diary will be accessed by participants using a hand-held device. When the participant reports development of a cold, a clinic visit will be scheduled as soon as possible (within 48 hours of cold symptom onset) to collect blood and nasal samples. A second clinic visit will occur 4-6 days from the onset of cold symptoms to obtain samples after the initial cold, but prior to the use of systemic corticosteroids. Participants will be followed for up to two colds or approximately 6 months after Visit 0, whichever comes first.