In many cases people with asthma are sensitive to a number of different allergy-causing substances and irritants. They may not develop an asthma attack until they encounter a combination of triggers, e.g. exercise and cigarette smoke, car exhaust fumes and cold air.
Often, the trigger takes the form of an allergic reaction to a substance which is generally regarded as harmless. Thus, while most people may be able to walk through a newly mown field, an asthmatic who is allergic to grass pollen will start to gasp and wheeze.
If allergic reactions occur in the skin they cause rashes such as eczema, dermatitis and urticaria. When they occur in the eyes and nose (e.g. with hay fever, rhinitis), those organs start to itch and stream. It is not uncommon for people with asthma to have other allergic conditions as well.
The commonest allergic triggers are house dust mites, pollen, animals, mold spores, drugs, chemicals and food.
However, asthma attacks also occur after exposure to a range of non-allergic triggers, including virus infections, exercise, change in temperature, emotional stress, air pollution, hormonal changes (in women) and tobacco smoke.
Many people with asthma have a combination of triggers, allergic and non-allergic. Because of this, doctors are now less inclined to make the distinction between allergic (intrinsic) and non-allergic (extrinsic) forms of asthma.
Asthma can be treated by breathing in (inhaling) medicine straight into the lungs. In this way, it can be taken in low doses with minimal side-effects. There are many types of inhalers, including aerosols(puffers), and dry powder devices, which are good for administering preventer treatment to children over three years.