Cause

The cause of asthma is not known. Health experts believe that inherited, environmental, and immune system factors combine to cause inflammation of the bronchial tubes, which carry air to the lungs. This can lead to asthma and asthma attacks.

• Asthma may run in families (be inherited). If this is the case in your family, you may be more likely than other people to develop long-lasting (chronic) inflammation in the bronchial tubes.
• In some people, immune system cells release chemicals that cause inflammation in response to certain substances (allergens) that cause allergic reactions. Studies show that exposure to allergens such as dust mites, cockroaches, and animal dander may influence asthma's development.¹ Asthma is much more common in people with allergies, although not all those who have allergies develop asthma. And not all people with asthma have allergies.
• Environmental factors and today's germ-conscious lifestyle may play a role in the development of asthma. Some experts believe that there are more cases of asthma because of pollution and less exposure to certain types of bacteria or infections.² As a result, children's immune systems may develop in a way that makes it more likely they will also develop allergies and asthma.

Asthma in adults also can be related to work (occupational asthma). Being around animals, plastic resin, wood dust, grain dust, insecticides, and metals can cause asthma, usually because your immune system reacts to the material. Some people continue to have asthma symptoms even after they are no longer exposed to what caused the symptoms. But for many people, symptoms will get better or go away when they are away from the asthma trigger.