Bloat

• Bloat is a serious medical condition that occurs when too much air gets into the abdominal cavity of a dog. Coughing up white foam can be a symptom of bloat and should be checked out immediately as it can be fatal.
  
  

Infection

• Fungal infections can cause a dog to cough up a white frothy liquid. A dog might pick up a fungal infection from eating something containing fungus or bacteria.
  
  

Excitement

• Some dogs cough up white froth simply because they are overexcited. For dogs who are prone to this, refraining from getting them worked up can help tremendously.
  
  

Hormones

• Pregnant dogs might cough up white froth due to a change in their hormone levels. While it is not something to worry about, repeated coughing should be investigated further.
  
  

Kennel Cough

• Kennel cough, or Bordatella, can cause a dog to cough up a white foam. Dogs who live in shelters, or have recently been boarded are most likely to suffer from kennel cough.
  
  

Tonsillitis

• Tonsillitis can often cause a dog to cough up a white froth. Tonsillitis is more common in small dog breeds than large ones, and can be treated with a course of antibiotics.