Patients with allergic asthma usually have a family history of allergies and a past medical history of eczema or allergic rhinitis. Exposure to the allergen triggers an asthmatic attack. Idiopathic or non-allergic asthma is not related to specific allergens. Factors such as a common cold, respiratory tract infections, exercise, emotions, and environmental pollutants may trigger an attack. 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.