Why do some people develop asthma all of a sudden?

It happens!: Asthma can follow any number of "insults" to the lungs. This can occur after a large exposure to a chemical irritant or other allergens present at the workplace. Asthma can also begin after a lung infection/bronchitis, especially viral illness. The latter is more often seen in children.

The domino effect: In true asthma you have the genetic tendency present from conception.How or if you ever emerge in active disease will depend on a series of life events or triggers that allow it to emerge. Some of the more severe cases will emerge in childhood, but some do not occur until much later.Having a 1st wheezing episode at 70 is not unheard of.It happened in my family.