If a dog vomits white foam, it usually signals gastrointestinal distress. Foamy vomit might occur if your dog has a lot of gas in their stomach. This may be due to something as simple as eating grass or eating fatty foods that irritate their digestive tract. However, it's also possible for foamy vomit to signal a more serious problem. Kennel cough, for example, can cause foamy vomit in dogs. Tracheal collapse, bloat, acid reflux, and kidney problems can also result in foamy vomit. If your dog is vomiting foam, make sure to check them for other symptoms of illness and call your vet. Your vet can prescribe dog anti-vomiting medications to help.