Can think of two reasons.

1/ Is just a craze kids go through. It has passed now in English speaking countries.
Nonenglish speaking ones have just caught onto it.

2/ The asthma gene is regressive. Asthmatics have less loving, so have fewer kids.

Mind you, was pretty scary when a kid at my house started to wheeze !!!

I had an asthma attack while playing tennis once. I swallowed some saliva down the wrong tube. It's pretty scary not being able to breath. But I don't see how you could over-diagnose it. Joke?

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http://www.smh.com.au/news/World/Doubts-cast-on-hygiene-hypothesis/2007/10/07/1191695716386.html

The idea that an increase in allergies and asthma is a result of a reduction in childhood infections seems not to hold up, researchers report.

Preventing common respiratory infections and stomach infections in child daycare centres had no impact on the later development of asthma, nasal allergies or eczema, according to a follow-up survey conducted 12 years later.

The findings do not support the "hygiene hypothesis," which theorises that reduced exposure to infections in childhood leads to greater allergic sensitisation, conclude Dr Teija Dunder and colleagues from the University of Oulu, Finland.

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Housework 'could pose health hazards'

http://www.smh.com.au/news/World/Housework-could-pose-health-hazards/2007/10/15/1192300650086.html

Housework might be bad for your health, according to a study suggesting that tidying up as little as once a week with common cleaning sprays and air fresheners could raise the risk of asthma in adults.

Other studies have linked these types of products with increased asthma rates among cleaning professionals but the research published on Friday indicates others are potentially at risk as well.

Exposure to such cleaning materials even just once a week could account for as many as one in seven adult asthma cases, the researchers wrote in the American Journal of Respiratory and Critical Care Medicine.

"Frequent use of household cleaning sprays may be an important risk factor for adult asthma," Jan-Paul Zock, an epidemiologist at the Centre for Research in Environmental Epidemiology in Barcelona, who led the study, wrote.

Asthma is an inflammation of the airways with symptoms that include wheezing, shortness of breath, coughing and chest tightness. More than 300 million people worldwide suffer from the condition.

Using data collected from 22 centres in 10 European countries, the researchers studied more than 3,500 people over a nine-year period to see how many developed asthma and whether cleaning could be a cause.

Two-thirds of those in the study who reported doing the bulk of cleaning were women and fewer than 10 per cent of them were full-time homemakers, the researchers said.

The study found that the risk of developing asthma increased with the frequency of cleaning and the number of different sprays used but on average was about 30 to 50 per cent higher in people exposed to cleaning sprays at least once a week.

While air fresheners, furniture cleaners and glass-cleaners had the strongest effect, the researchers said the study did not determine what biological mechanism sparked the increase.

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Manure might be key to kicking cancer

http://news.smh.com.au/manure-might-be-key-to-kicking-cancer/20080128-1oiu.html

Farmers can breathe easy after scientists discovered that working with manure can drastically reduce chances of developing lung cancer.

New Scientist magazine reported dairy farmers were five times less likely than the general population to develop the disease.

It found farmers typically breathed in dust that consisted largely of dried manure, and all the bacteria that grew in it.

"As strange as it sounds, epidemiologists are starting to uncover unexpected links between our exposure to dirt and germs, and our risk of cancer later in life."