I believe there are 4 primary ways to go about this:
There has been research and experiments done on genetic engineering to shutdown specific proteins.
Common types of antihistamines are Seldane, but it provoked cross reactions with other medications so now it is being marketed as Allegra, which has less or none of the side effects of Seldane which were causing problems previously. There's also Cetirizine, Loratadine, etc. Sometimes one medication works while another doesn't, so don't hesitate to try others if you feel like the one you're using isn't being too effective. Of course, do consult a professional in the field if you are able to.
For asthma, leukotrienes are chemicals that can be released by white blood cells and can trigger the asthma. Ventolin is the most common inhaler, it works like adrenalin, but has less effects on our hearts.
You can also go for allergy testing, but that's not really fool proof though...
If avoidance doesn't work, and antihistamines don't work either, then you could try to opt for allergy shots. These could be altered forms of the allergen, and tiny amounts get injected into your body. This would allow for the reduction in the IgG antibody of the ones responsible for the allergic reaction, and therefore prevents IgE to the allergen.