It is still unknown exactly what causes asthma . It can be cause by a number of things.
Researchers have not found a particularly cause of it but have point of a number of reasons that could lead to why you inherit it.
As those reasons are well known factors to cause the disease, it still could be something completely different to have caused it.
Researchers said that it is more likely for a child to get this disease in places like developed countries than in third world countries. They came up the theory that children are less likely to develop the diseases in the third world countries because they bodies develop a stronger immune system than in develop countries.
It is called the "Hygiene Hypothesis"
The reason is that develop countries are so modern in terms of their clean environment that they don’t really get the chance to fight as much bacteria’s and viruses etc, as they would in the none develop countries.
However this theory can be debatable.
It is also said that children who are given antibiotics stand a much better chance of not developing the illness than those who do. This is to do with strengthening the immune system from a young age.
Again it is difficult to know exactly what causes this respiratory disease but these could have possibly be part of the reason.
You can also develope the disease in adulthood, which is called adult onset. It can be caused by a long history of chest infections and other respiratory conditions.