You may have already looked into this, but I would guess that your husband has food allergies . Personally, I used to get "hayfever" allergies but then found that when I cut out wheat and dairy and other allergen foods, I stopped sneezing. Now I sneeze after eating these types of foods. My best recommendation would be to look into the "blood type" diets, in Dr. D'Adamo's book "Eat Right For Your Type". This is the diet that completey cured me of my allergies and I feel it is really accurate in eliminating "allergen" foods for each blood type.
Another thing to look into would be candida--read about it on the candida homepage of this site. Candida (and parasites) make you a lot more susceptible to food allergies . You can do the candida tests to see if your husband has symptoms, and then see if some candida remedies help. Candida is also treated with a simple diet, so that will help the allergies as well..