If you have a certain kind of allergic antibodies in your circulation and if they are coated onto a special cell (a basophil) in a lung, and if that antibody-coated basophil encounters its matching allergen, then the activated cell will release a host of biochemicals. Some of these will cause smooth muscle in the walls of nearby air passages to tighten and constrict and will stimulate the release of mucus. Both of these processes lead to coughing and wheezing and make breathing difficult—in short, an asthma attack.