A dog's mouth may foam for several reasons, ranging from harmless to serious. Common causes include ingestion of something bitter or toxic, dental disease, heat stroke, nausea, stress or anxiety, overexertion, motion sickness, seizures, gastrointestinal issues, and in rare cases, rabies if not vaccinated. Foaming often happens due to excessive drooling combined with panting, which creates a foamy texture. If the foaming is accompanied by other symptoms like vomiting, seizures, confusion, or if the dog has potentially ingested toxins, it is important to seek veterinary care immediately. However, foaming can also be benign, such as after heavy exercise or due to anxiety. In summary, foaming may be caused by:

• Ingesting bitter or toxic substances
• Dental or oral health problems
• Heat stroke or overexertion
• Stress, anxiety, or nausea
• Motion sickness or seizures
• Rarely, infections like rabies (mostly if unvaccinated)

If the cause of foaming is unclear or concerning, contact a veterinarian promptly for diagnosis and treatment.