Asthma is not contagious, according to the Palo Alto Medical Foundation. Asthma is a chronic condition caused by the swelling of airways, which leads to difficulty breathing, notes Medline Plus. Some common asthma triggers include dust mites, pet hair, cold weather, mold and pollen.
Many people who have asthma also have a family history of allergies, such as hay fever, explains Medline Plus. People with asthma typically have swollen bronchial tubes. Asthma triggers cause the muscles in these airways to tighten, which prevents air from passing through them to the lungs. This causes an asthma patient to wheeze and feel a shortness of breath, reports WebMD.