Asthma affects the airways in your lungs. The mucus that is normally present becomes thick, sticky and is present in greater amounts. The muscles around the airways tighten. All of these things make the airways narrower partially blocking the flow of air and often making it hard to breathe. You need to know the ways asthma affects the airways so you can understand why it often takes more than one kind of medicine to treat the condition.
Some medicines relax the tight muscles while others reduce or prevent the swelling and mucus.
The basic cause of asthma is not yet known. People with asthma have airways that are affected by things that do not bother people who don't have asthma. Respiratory infections such as colds and flu. Exercise, especially running or vigorous play. Irritants such as smoke or strong fumes or odors.