Nasal discharge is simply any fluid emitting from your dog’s nostrils. Nasal discharge can result from a number of conditions that cause an excess of fluid production in your dog’s nose, nasal passageways, sinuses and lungs. These include infections (fungal, parasitic, bacterial or viral), pollutants, allergies, nasal tumors, sinus tumors and dental infections. A visit to the vet is important to determine the underlying cause.