Interestingly enough, I started taking vitamins. And not just something you find at your corner store. These are pharmaceutical-grade, meaning they are of much higher quality and more potent.
After much testing on myself, what has worked for me is a multi-vitamin, grape-seed extract, and a calcium/magnesium supplement. It took about 3-4 months for the full affect to take hold. But I've never looked back since I started taking them.
My wife and I actually went into the business of selling these supplements to help out others. We've found the success stories aren't limited to simply allergies either. We're quite impressed with the results.
I can't guarantee it will work for your husband, but if you feel as though you would at least like some more info, just let me know.