One-half of asthmatics start to suffer in childhood, one-third between the ages of 15 and 44 (adult onset) and the remainder (one-sixth) after the age of 45 (late onset).

Asthma cannot be cured but could be controlled.The strongest risk factors for developing asthma are exposure, especially in infancy, to indoor allergens (such as domestic mites in bedding, carpets and stuffed furniture, cats and cockroaches) and a family history of asthma or allergy.

Exposure to tobacco smoke and exposure to chemical irritants in the workplace are additional risk factors. Other risk factors include certain drugs (aspirin and other non-steroid anti-inflammatory drugs), low birth weight and respiratory infection. The weather (cold air), extreme emotional expression and physical exercise can exacerbate asthma.

Urbanization appears to be correlated with an increase in asthma. The nature of the risk is unclear because studies have not taken into account indoor allergens although these have been identified as significant risk factors.

Because asthma is a chronic condition, it usually requires continuous medical care. Patients with moderate to severe asthma have to take long-term medication daily (for example, anti-inflammatory drugs) to control the underlying inflammation and prevent symptoms and attacks. If symptoms occur, short-term medications (inhaled short-acting beta2-agonists) are used to relieve them.

Medication is not the only way to control asthma. It is also important to avoid asthma triggers -- stimuli that irritate and inflame the airways. Each person must learn what triggers he or she should avoid.

Although asthma does not kill on the scale of chronic obstructive pulmonary diseases (COPD), failure to use appropriate drugs or comply with treatment, coupled with an under-recognition of the severity of the problem, can lead to unnecessary deaths, most of which occur outside hospital.