Why Is My Cat Throwing Up Milky Stuff. The toxic substance can cause a reaction and also dehydrate the cat, leading to foam residue. There is a world of reasons why your cat might be exhibiting this behavior.
Sometimes a change in diet, even treats, can cause an upset stomach. This is common, but if it happens all the time, consult with your veterinarian. Furballs, parasites, and food allergies are common causes of inflammation.