Raisins are bad for dogs because they cause a toxic reaction in the body. Such toxic reactions can lead to kidney failure, according to the ASPCA. Dogs of any breed and age may be affected if they eat raisins.
It is not yet clear why raisins are harmful to dogs, causing them to vomit and have diarrhea. Dogs also lose their appetite and may suffer from abdominal pain after eating raisins. Excessive consumption of raisins can cause a decrease in urination. Kidney failure may lead to the death of the dog after 3 or 4 days. Keeping grapes and raisins away from dogs helps to keep them healthy.