Dairy and congestion?

MY SON IS 5 AND HAS SEVERE ALLERGIES AND ASTHMA. MILK AND DAIRY MAKES THESE THINGS WORSE. IF HE IS STOPPED UP AND DRINKS MILK IT JUST SEEMS TO MAKE HIM EVEN MORE STOPPED UP AND CAUSES MUCUS TO CLOGGED UP HIS THROAT. I DONT KNOW ANYTHING ABOUT DAIRY ALLERGIES THOUGH. YOU COULD CONSULT YOUR DOCTOR ON THAT PART OR DO SOME RESEARCH ON DAIRY ALLERGIES.