This is very common in bulldogs… where are the hives located? First of all you can give him benadryl 25mg tab, depending on his weight I usually give my bully one tab twice a day. My bullies have gotten hives from bee stings, food, environmental allergens… it really can be anything. If he has them on his face PLEASE watch him carefully, if they get worse (or his face is super swollen) he will need to see a vet ASAP!!! It could cause breathing issues and become an emergency. Have you used any new cleaners, laundry detergents, pet shampoos?!!