Puppy Tear Duct Inflammation. Dog tear stains tend to be. When the ducts are infected or blocked, they can become swollen.
Putting a teaspoon of apple cider vinegar in your dog’s water (he won’t even notice) can help clear up the tear ducts quickly. This overflow of tears can lead to moisture and tear staining below the eye. Other causes of tear duct blockage include hair, dust or other debris in the tear ducts and inflammation caused by infection.