Human biology.. asthma questions..PLEASE.. help..?

Asthma is a breathing disorder characterized by an involuntary contraction of the muscles in the trachea and bronchi in the lungs. This restricts breathing and the victim begins to suffocate. Asthma can be the result of a great many different things but to the best of my knowledge nobody knows the exact cause. Victims generally inhale a muscle relaxer to reopen their windpipe. Asthma may be an allergic response to a particular substance. Determining what it might be involves removing anything in the environment which may cause an asthma attack and then recording the frequency of any subsequent attack. The hypothesis is that a decrease in the occurrence of asthma suggests the things eliminated from the environment are involved in the attacks.