The underlying cause of asthma is unknown, but most cases tend to be inherited and it occurs more frequently in those who suffer from allergies. There are a wide variety of things that can trigger wheezing in those with asthma.

There are two main types of asthma:

• Allergic asthma: also known as extrinsic asthma, this type is triggered by an allergy. Many people with this form of asthma have seasonal symptoms when their allergies are at the worst.
• Non-allergic asthma: also known as intrinsic asthma this type of asthma can also be triggered by things like exercise, stress, and exposure to cold air.

In all cases, asthma causes swelling and inflammation in the airways within the lungs. When an asthma attack occurs, the airways become narrower leading to wheezing.