Why is my cat throwing up white foam?

White or clear foam is usually stomach fluid and mucus brought up on an empty stomach, often when too long has passed between meals or after a bout of nausea. An occasional foamy vomit in a cat who’s otherwise normal isn’t an emergency, and smaller, more frequent meals can help if it tends to happen overnight. What changes the picture is repetition. Foaming several times, bringing up foam plus food, or pairing it with lethargy, no appetite or diarrhea means it’s time to call the vet rather than wait.

When to call a vet: Repeated foamy vomiting, or any vomiting with lethargy, appetite loss or diarrhea, warrants a vet visit.