Triggers may inflame the airways to the lungs, allowing disease-fighting cells to accumulate and causing swelling in the lungs. In addition, the airways may become blocked or obstructed when the muscles surrounding the lungs tighten or go into spasm. This keeps air from circulating freely in the lungs. Or, mucus may clog and narrow the airways in the lungs, making breathing even more difficult. During an asthma attack, the walls of the airways become inflamed, and the mucous membrane covering the walls becomes swollen with fluid.
Sticky mucus fills the remaining space, making it difficult to breathe.
Because air cannot flow in and out of the lungs freely, a whistling or wheezing sound may be heard. During severe attacks, wheezing may stop because there is too little air moving to make any noise. Asthma attacks can be mild, moderate, or severe, and can last for a few minutes, a few hours, or several days. They can occur anywhere and at any time. Many occur at night.