Researchers have this week got a step closer to understanding asthma, and have pinpointed two likely causes.
The first is the modern lifestyle of most children, who sit for hours in front of a tv or computer screen, and the second is pollen and mould.
Researchers from Glasgow University reckon that children who sit in front of a television double their risk of developing asthma. Not that the television itself is to blame, it's simply that children aren't getting outside to play and exercise, and so breathing fully.
In a study of 3,000 children, who were tracked from birth to the age of 12 years, researchers found a direct relationship between the amount of television watched and asthma. Those who watched television for two hours or more a day were nearly twice as likely to develop asthma.
Sitting around may encourage shallow breathing where the lungs are not fully functioning, say the researchers.
In the second study, researchers have found a direct link between the disease and newborns whose first few months of life are during the late spring or winter, when pollen or mould are at high levels.
Those whose first months of life were in the late autumn or winter were three times more likely to develop wheezing, often an early sign of asthma, than those born in the high summer, after the pollen levels had fallen.
Researchers examined the health of 514 children born between 1999 and 2000 in California's Salinas Valley, where ambient mould levels began to increase in November and December and pollen levels peaked in March and April.
(Sources: TV study: BBC website, March 3, 2009; mould study: Thoraz, 2009; doi: 10.1136/thx.2007.090241).