Asthma is a disease involving airway inflammation. It is characterised by airway hyperresponsiveness and attacks of reversible airway obstruction.
Asthma is a chronic respiratory illness of enormous public health significance. There have been substantial increases in asthma prevalence, morbidity, and mortality throughout the world beginning in the 1970s. It is the only treatable disease whose incidence is on the increase throughout the world, and particularly in developed and industrialized countries.
Children are the most vulnerable; increased incidence of childhood asthma contributes to the overall trends. Some experts put part of the blame on the increasingly sterile conditions in which children are growing up. Smaller families, less exposure to infections and more antibiotics early in life may be shaping children's immune systems to overreact to normally harmless irritants.
Other reasons are not well understood, notably with respect to adult asthma. There is a link with overweight. It is also suggested that environmental factors are significant factors. Indoor air quality also plays an important role, and the roles of house dust mite allergy, humidity or moulds, and cockroaches have been well established. Outdoor air pollutants (such as particulates, ozone and sulphur dioxide) may exacerbate asthma, and children living along busy roads have increased rates of respiratory symptoms and declined lung function. Many non-specific stimuli such as exercise, cold air or passive smoking can trigger attacks. These responses to otherwise "trivial" stimuli such as cold air are referred to as bronchial hyperresponsiveness.
If asthma is caused by obstructed respiratory system it is said to be bronchial; if red blood cells fail to carry oxygen away from the lungs, it is cardiac. The three cardinal features of bronchial asthma are shortness of breath and other signs of oxygen deficiency (such as laboured breathing blueness of lips or a rapidly beating heart); wheezing (a unique sound made by air passing through narrowed, mucus-filled bronchi); and coughing, a reflex that produces expectoration. Asthma has specific causes (such as allergies and infections) but heredity, environment, hormones, diet and stress are important factors determining its course. This disease has a high morbidity with a surprisingly low mortality, though its treatment may have negative side-effects.
The first asthma case reported dates back to 1910, when a child was admitted to a UK hospital for respiration problems. The disease was rare, however, until just after the First World War. While pollutants such as sulphur dioxide, ozone and sulphuric acid can damage lung function, air pollution in general has lessened since the 1950s in most cities. Cigarette smoking is decreasing and the prevalence of the main domestic allergens, house dust mites and cats, has not changed substantially since the 1960s. Recent studies in Germany and the USA have found no link between asthma and pollution. The indications are that an "immuno-deficient diet" (low in fresh fruit and vegetables may be a more significant environmental cause of asthma).
The airway inflammation that marks asthma is often caused by an abnormal immune reaction to environmental irritants such as pollen, dust and mould. Studies have suggested that certain infections early in life may ward off asthma by pushing the developing immune system toward infection-fighting mode. This, the theory goes, may make children's immune systems less likely to overreact to normally benign environmental factors. German investigators have found that repeated "mild infections" of the upper respiratory tract – runny nose or infection with a herpes virus – are linked to a lower risk of asthma and allergy. On the other hand, repeated infections of the lower respiratory tract, such as the flu or pneumonia, were associated with a higher asthma risk.
Globally, the prevalence of asthma has doubled between 1974 and 1994. A 1993 report shows that asthma is more common in highly developed areas, as it is 10 times more common in Australia than in China, and seems to increase in Africans only when they migrate to the cities. In the UK it causes 2,000 deaths a year (1993), where asthma is the greatest single cause of hospital admissions after heart disease and strokes, and sends more children to the hospital than any other complaint. It is also the leading reason that children miss school and adults miss work.
In the USA from 1982-1992, the age-adjusted prevalence of asthma increased by 42%, while the overall age-adjusted mortality rate for asthma during the years 1982-91 increased by 40%. In the 1990's, between ten to 15 million Americans suffered from varying degrees of asthma and in 1999 over 5,000 a year died from it (an increase from 2,598 in 1979). Many are African-Americans, who die from the condition at a rate six times that of Caucasians. In 1990, asthma was estimated to create an economic burden of six billion dollars in health care expenditures. Asthma is the most common chronic condition of childhood, affecting approximately five million children, and is the most common cause of hospitalization of children. Some believe that about 10% of all children may be affected, but good statistics demonstrating the variability of asthma prevalence by region of the country do not yet exist. Asthma attacks are the number one cause of school absenteeism and that childhood asthma has increased 75% between 1980 and 1994.
In Canada, asthma affected 2.5 percent of children in 1978. By 1994, it was affecting 11.2 percent of children. The reasons are unclear but are linked to air pollution.