first thing is you have to avoid substances which are allergic to him like dust , pollen , some foods. keep his room and clean.
then daily doing exercise will reduce allergy.
and allergy specialists are there. you go them they will do a prick test . and identify for which allergen you allergic. for which they will give immunotherapy for 3 years . its permanent solution
you have to take once in week . in bangalore its available in kims hospital.