Fluticasone is a strong man-made steroid that binds tightly to the body's steroid receptors. In the airways, it calms many kinds of immune cells, such as mast cells and eosinophils, and the chemical signals, such as histamine and leukotrienes, that drive inflammation. With less inflammation, the airways become less swollen and irritated, which makes breathing easier.
It acts locally in the airways, and almost none of the part that is swallowed reaches the bloodstream. Symptoms may start to improve about 24 hours after starting, but the full benefit can take 1 to 2 weeks or longer, so it does not help during an attack. It can let a yeast infection grow in the mouth and throat, and because steroids dampen the immune system, it can make some infections more serious. With long-term use, it can also lower bone density and slow growth in children.