Q. My dog threw up white foam stuff what causes that
A. White foamy vomitus is usually saliva and mucous that he has swallowed and it usually means his stomach was empty if he vomited. If he was coughing and gagged afterward, this could also explain the white foam. Watch him carefully, if he starts to feel bad, continues vomiting, loses his appetite, or develops diarrhea or fever, get him seen by your vet right away. He could have eaten something that disagreed with him, ingested some kind of foreign substance or toxin, may have been too active after drinking water, there are a number of possibilities.