The generally accepted belief, is, it's the enzyme, within the gut of the microscopic Mite that causes Asthma, but it might just be a trigger, like fine dust, or other airborne allergens.
It's more likely, that the problem, is genetic, but can be controlled, through changes in breathing and some physical therapies ( not physiotherapy )
Sprays, cleaning regimes, better airflow, in homes can all help to control Asthma, but won't eliminate Asthma, whereas the changes in breathing technique and specific physical therapies can.
There will always be occasions, when changes in diet alone, will eliminate what appears to be Asthma, but has been an allergic reaction.
As Phil says, open your windows, allow the cool air to circulate through bed sheets and turn off bedroom heaters.
Obviously, it's a good thing, to have mattresses vacuumed regularly and products which have proven to kill dustmites have to be a good thing.
But............don't claim to have a cure for Asthma, even therapists, like myself never claim, to " cure "it's not allowed, even with a list of clients, whose lives have been changed, some, for years, it's not allowed to claim, that you can "cure"
