Why do my dog's eyes discharge?

Dog's eyes may discharge for several reasons. Tearing may be from an irritant in the area, such as dust. Allergies, viral diseases, and problems with tear drainage can cause runny eyes. Thick, colored discharge can be from bacteria, or viruses that unable a dog to make enough tears. The bottom line is that you should have your dog's eyes examined by your vet to determine the specific cause and treatment.