vitamin C - natural antihistamine

Well as the title says really

Giving your dogs vitamin C tablets (not the chewy orange flavoured ones) is a natural way to give them an antihistamine. Only side effect known is diarrhoea, so feed according to bowel tolerance, meaning you can give a few every day should your dog not get diarrhoea from it etc...

more accurately it is the quercitin in the Vitamin C complex that is the antihistamine. The FDA defines Vitamin C as ascorbic acid, but the ascorbic acid is the part of the Vitamin C complex that acts as an antioxidant and preservative for the very delicate bioflavonoids. (In nature, Vitamin C-ascorbic acid alone does not exist.)

http://www.healingnaturallybybee.com/articles/allergy2.php