“Extrinsic” asthma is characterized by symptoms that are triggered by an allergic reaction. It is the most common form of asthma. It occurs more in children asthmatics. About 90% of childhood asthma cases are due to inhaled allergens e.g. dust mite allergen, pet dander, pollen, mold etc.
Skin tests and blood tests often reveal presence of an underlying allergic diathesis, with positive skin reactivity to common allergens, increased eosinophils count, total or specific IgE level in blood.
Individuals often have other evidence of atopy, such as allergic rhinitis or eczema.
Family history of atopy is often positive.
A lot of patients have a mixed form of asthma that is triggered by allergens together with conditions like extreme cold and by chemicals.