Styrofoam is not digestible and can get stuck in the dog's intestines, causing a blockage. If not treated, the blockage can kill the dog. Ingested Styrofoam can also cause damage to the intestines and other internal organs as it passes through the dog.
Small amounts of Styrofoam may pass through the dog without causing injury. Dogs who consume Styrofoam should be examined by a veterinarian to determine if the Styrofoam has lodged within the digestive tract or has caused damage to internal organs. Styrofoam can also cause choking, if a dog accidentally inhales some of it while trying to eat it.