Smoking can trigger asthma because when a person starts inhaling tobacco smoke it irritates substances that settle in airways that are moist with lining. The substances that it settles is what triggers the attack if the person has asthma.

Tobacco smoke can damage little hair structures located within the airways. These hair like structures are known as the cilia. The cilia is very important in the body because it can sweep the mucus plus dust from airways. When smoke settles in the cilia it can not work the way it should causing the mucus plus dust to start accumulating within the airways.

Smoking causes lungs to create and make a lot of mucus and more so than usual. When more mucus builds inside airways it can trigger asthma attacks. When a person who has asthma has an attack it can be very harmful to their body and sometimes even cause death. If someone has asthma they should avoid being around tobacco smoke so it won't cause an attack.