Asthma attacks may become more severe and frequent with time, and can progress to chronic bronchitis or emphysema. Mixed asthma is the most common form of asthma. It has characteristics of both the allergic and the idiopathic or non-allergic forms. Asthma is a reversible diffuse airway obstruction. The exact mechanism of these changes is not known, but most of what is known involves the immune system and the autonomic nervous system.
Some asthmatics develop exaggerated responses.
The release of mediators in the lung tissue affects the smooth muscles and glands of the airway, causing bronchospasm mucous membrane swelling, and excessive mucus production. Bronchoconstriction can be caused by such factors such as exercise, cold, smoking, emotions, and pollutants. These same factors also stimulate the release of histamine. Consequently, asthmatics are prone to an increased release of chemical mediators and constriction of smooth muscle in the lungs. They also increase ciliary movements, decrease chemical mediators and potentiate the effects of corticosteroids.