In this type of asthma, the cause of an attack is normally the inhalation of an allergen . In extrinsic asthma, the reaction of the airways is like an allergic reaction , and is similar to hayfever and other allergies. They colonise houses, especially in warm, humid areas. They tend to live in carpets, mattresses, pillows and soft furnishings. Although quite harmless, their droppings contain substances that are allergens.
Inflammation is the process that makes living tissue swell, become painful and turn red.
Inflamed tissue contains damaged cells and has a higher than normal blood flow through it - that is why it s red and warm. It is usually infiltrated by many cells of the immune system. Inflammation is often associated with infection but it can also be caused by allergic reactions. One of the major inflammatory cells in asthma is the eosinophil, which can damage the airway lining. This can ultimately lead to permanent damage in the airways.