The cause of allergies to cats are coming from multiple factors:
1. Your husband is eating processed foods/junk food which destabilizes the immune system, leaving him weak to defend against the cat dander.
2. The cat is not fed a species appropiate diet thus leading to a weak immune system in the cat which leads also to the shedding of cat dander often. I read in a book with herbal remedies for cats where a vet technician had allergy attacks when going to a cat colony to treat the cats. The cats were on kibble food. After the owner of the cat colony switched them to the species appropiate diet, the vet technician didn't get anymore the allergy attacks when visiting the cat colony.