Many asthma triggers have been identified, but the real cause of asthma is unknown. What is known is that the airways - or bronchial tubes - of asthmatics are unusually sensitive to a variety of substances, such as allergens and some chemicals. This sensitivity is often referred to by doctors as 'bronchial hyper-reactivity'. People born with bronchial hyper-reactivity respond to triggers that normal people don't even notice. However, the basic abnormality that distinguishes the asthmatic from the non-asthmatic is still unknown.
Asthma can develop at any age. It can develop suddenly, at any stage of life, even in elderly people who have never experienced any symptoms previously. Adult onset of asthma is usually more persistent than childhood asthma, causing more chronic symptoms and requiring long-term medication to keep it under control.
The severity and frequency of attacks vary from one individual to the next. Attacks strike people in different ways. They may start suddenly, without any warning, or develop slowly over hours or days.
Asthma symptoms also vary in individuals. Some people experience such mild symptoms that they are barely aware of any change in their breathing, while others must cope with severe and distressing symptoms. Some asthmatics experience symptoms over a long, unbroken period (sometimes lasting for months), while others have short attacks and are perfectly well in between.
