why asthma people have difficulties in breathing?

Answer 1

Asthma is an allergic reaction to some environmental or emotional trigger. Once the reaction is triggered two things happen 1) your bronchial passageways become inflamed and swell narrowing the airways 2.) The inflammatory response causes excess mucus to be produced.
Between the narrowed airways and the excess mucus asthmatics cannot get the oxygen they need. The narrowed airways causes the wheezeing sound when an asthmatic breathes.

Answer 2

lungs become constricted and air way passages tighten making it hard for you to catch your breath. When you use an inhaler like Albuterol it reverses the constriction and opens up the air passage so you can breath better.