Extrinsic or allergic asthma
About 80 per cent of children with asthma, and more than half of adult sufferers, have allergic asthma, which means their asthma is caused by coming into contact with a substance in their environment.
No one doubts that the hypersensitivity causing the muscles of the little bronchioles to constrict (and the tubes to become inflamed and filled with mucus) has to do with allergies. The conventional view maintains that the main culprits are grass pollen and the housedust mite Dermatophagoides pteronyssinus. This little creature is much more prevalent in homes today because of fitted carpets, heat and insulation. This type of asthma is also believed to be genetic. One-third of patients have a relative who has suffered from asthma.
Intrinsic or non-allergic asthma
This represents about 10 per cent of cases and usually develops after the age of 30. This form of asthma is not typically associated with allergies. The condition tends to affect women, and many cases seem to follow a respiratory tract infection. The condition can be difficult to treat and symptoms are often chronic and last all the year round.
Exercise-induced asthma (EIA)
Exercise has undeniable health benefits but, for a significant proportion of individuals, including professional athletes, exercise can be a trigger for breathing difficulties known as exercise-induced bronchospasm or, more commonly, exercise-induced asthma.
EIA is especially common in children and young adults, and comes on most often during intense exercise in cold, dry air.
EIA is not necessarily linked to an allergic reaction and you don't have to be asthmatic to have it, although many asthmatics do. US data suggest that asthma affects four to seven per cent of the population, and studies. People who only have EIA don't usually require long-term maintenance therapy. The condition tends to resolve itself shortly after exercise activity stops.
Adult or late-onset asthma
Asthma can start at any age, although it occurs more often in women, mostly middle-aged, and frequently follows a respiratory tract infection. Some people have symptoms during childhood, which then disappear in later life. Others develop late-onset asthma in adulthood without ever having had symptoms as a child.
Asthma can be difficult to detect in older people as some of the symptoms-cough, wheeze and shortness of breath-are shared with other conditions such as chronic bronchitis, emphysema, chronic obstructive pulmonary disease (also known as COPD) and heart disease.
Late-onset asthma is usually not caused by allergies, but can be brought about through infection. Doctors diagnose late-onset asthma when an adult develops chronic coughing and wheezing that does not appear to be caused by allergy, irritants or an obvious infection.