Stress & Anxiety. One of the most common causes behind foaming at the mouth in dogs is stress or anxiety. Stress in dogs can cause hypersalivation, often accompanied by panting and increased breath rates. Due to this, a dog's drool will often turn into frothing foam around their mouth.
What to do if my dog is frothing at the mouth?
If your dog is foaming at the mouth, it is recommended that you make an appointment with your veterinarian as soon as possible. Causes of foaming of the mouth in dogs can be due to mild issues or more severe issues, such as dental disease, a seizure or rabies infection.