With asthma, the airways in your lungs are often swollen or inflamed. This makes them extra sensitive to things that you are exposed to in the environment every day, or asthma "triggers." A trigger could be a cold or the weather, or things in the environment, such as dust, chemicals, smoke and pet dander.When you breathe in a trigger, the insides of your airways swell even more. This narrows the space for the air to move in and out of the lungs. The muscles that wrap around your airways also can tighten, making breathing even harder. When that happens, it's called an asthma flare-up, asthma episode or asthma "attack." Asthma can start at any age. Sometimes, people have asthma when they are very young and as their lungs develop, the symptoms go away, but it's possible that it will come back later in life. Sometimes people get asthma for the first time when they are older.