I have read that people with asthma frequently have lower than normal levels of gastric hydrochloric acid, which is of course important for proper digestion.
Supplementation with betaine hydrochloride, along with magnesium, B6 and B12 has helped many asthma sufferers.
As always, I recommend seeing a good nutritionist. Many things, such as Quercetin with Bromelain enzyme, plus Vitamin C,, are antihistaminic, and help stabilize cells to stop inflammation. B vitamin injections are also helpful.