Have you seen a touch-me-not plant? If you touch the leaves of this plant the leaves immediately curl up and fold.

The air tubes of an asthmatic are also oversensitive in a similar way.
They are oversensitive to a variety of stimuli: dust or pollens in the air, strong smells, weather changes, viral infections etc.

This causes a series of chain reactions which brings many cells and chemicals to the air tubes.

Collectively this leads to 3 important changes in the air tubes:

1. Contraction of the muscles around the air tubes.
2. Swelling in the inner most lining of the air tubes.
3. More phlegm production in the air tubes.

You can well imagine that all these changes lead to one thing – air way narrowing and reduced space for air to come into the lungs.

This is what causes wheeze and breathing difficulty. A normal person breathes without effort or being aware of breathing. For an asthmatic breathing becomes a major task. Imagine trying to drink coke from a straw which is all twisted up!

If these effects of asthma are not treated and are not well controlled it leads to this narrowing becoming permanent. This occurs after years of uncontrolled asthma.