Occasional clear discharge from the nose is normal, as the mucus lining keeps a dog's nose moist. Frequent, heavy or coloured nasal discharge or a drip accompanied by sneezing is usually a sign of an underlying illness or disorder. If your dog has bloody nasal discharge, seek veterinary care immediately as this could indicate a serious problem.
Upper respiratory viruses, including parainfluenza, distemper, bordetella and kennel cough, are common causes of nasal discharge. Most puppies' vaccine series protect against these common diseases, although dogs vaccinated against bordetella may still contract kennel cough. Usually, discharge is present from both nostrils. Other symptoms accompanying a respiratory virus include sneezing and watery eyes.
Dogs can experience allergies to pollutants, such as pollen or cigarette smoke, in the environment, as well as food allergies. Other symptoms, in addition to nasal discharge, include sneezing, rubbing the face and chewing the paws, as allergies often cause itchy skin in dogs. Your veterinarian can perform an allergy test, but this is usually not necessary in the case of seasonal allergies.
Fungus sometimes takes root and flourishes in the nasal passage. Nasal drip is often accompanied by blood when a fungal infection is present. A veterinarian may perform a culture to detect the presence of fungus, and the infection is usually treated with antibiotics.
In rare cases, a nasal tumour causes a dog's nose to drip. This is far more frequent in older dogs than in young dogs, and usually seen in dogs with long noses. A tumour may also cause unilateral bleeding--bleeding from one nostril. Most nasal tumours are malignant, or cancerous, but are sometimes treatable with chemotherapy.
If the roots of the teeth in the upper jaw become infected, the infection can spread to the nasal cavity. This may cause a mucus discharge from the nostrils. Dental problems are often detected through x-rays. In some cases, the solution may include extraction.
Occasionally, a dog may inhale an insect or other small object. This item becomes lodged in the nasal passage and is a source of irritation, causing nasal drip. Other signs may include bleeding from the nostril and pawing at the nose. A veterinarian can examine the nasal passage to detect and remove a foreign object.