ÙBenadryl is an antihistamine with the active ingredient diphenhydramine. It can provide your dog temporary relief for allergic reactions caused by bee stings, insect bites, vaccinations, snake bites and can provide relief if your dog is itching because of a flea allergy or food allergy. If you give your dog Benadryl for itching associated with a food allergy, it will only treat the symptoms for a short time. You will still need to take your dog to a veterinarian for a definitive diagnosis and treatment.