What they do know is that asthma rates since around 1900 have skyrocketed. In fact, just within the past 20 years asthma rates have increased over 250%.
For many people, asthma, allergic rhinitis (hay fever) and dermatitis (eczema) go hand in hand. In 2006 the faulty gene that causes these diseases was isolated, which brings about hope that some day a cure may be found.
Despite the fact that only people with the "faulty gene" can develop asthma, eczema or allergies, the reciprocal is not true: not all people with the faulty gene will develop these illnesses.
Children who were exposed to Rhino virus had a 6% less chance of developing allergies, and those exposed to dogs had a 50% less chance, and those exposed to farm animals such as pigs, grew up in large families, had cats as pets, spent time in day care were also less likely to develop allergies.
Likewise, in less developed nations where children have a greater likelihood of being exposed to "poor hygiene", asthma rates are almost insignificant. Thus, asthma is basically a disease of the developed world: the United States, Western Europe, Australia and New Zealand.
In 1989, these and other observations led to one scientist developing the hygiene hypothesis, which simply states that by not being exposed to bacteria, viral infections and endotoxins has increased the likelihood that children with the "faulty gene" will develop some form of asthma.
According to Dr. Joseph Mercola, "exposure to certain types of infectious agents and endotoxins is essential for maturation of the immune system, and that less exposure leads to an imbalance of certain types of immune responses."
And this leads to the body developing antibodies against innocuous allergens and basically attacking itself, and causing the owner of the body to suffer.
Right now the goal is to prevent and treat the symptoms. Someday, however, there may be an outright cure for asthma, or at least a way to prevent future children from getting the disease.