Asthma
A chronic inflammatory airway disease causing reversible bronchospasm and mucosal swelling that narrows the airways episodically, so triggers, variability and reversibility (not fixed obstruction) define both the symptoms and the treatment ladder.
First principles
Asthma is airway hyper-responsiveness, not a fixed structural lesion
In sensitised airways, exposure to a trigger (allergen, cold air, exercise, viral infection) activates mast cells and eosinophils, releasing histamine and leukotrienes. These cause three things simultaneously: bronchial smooth muscle spasm, mucosal oedema and increased mucus secretion. All three narrow the airway lumen, but crucially all three are reversible: smooth muscle can relax, oedema can subside, mucus can clear. This is the fundamental difference from COPD: the obstruction is a functional, inflammatory process superimposed on airways that are structurally normal between attacks, which is why symptoms are variable and a bronchodilator can substantially reverse them.
Educational content pending clinical review. Not medical advice.