In the broadest sense, it is a myth that a dog with a cold wet nose is healthy and a dog with a warm and dry nose is ill. However, the appearance, color and other factors regarding a dog's nose can help to diagnose various ailments.
A well-hydrated dog has the required amount of blood supply to the nose, making it moist and cold to the touch. Conversely, a warm dry nose when combined with symptoms such as vomiting or loose stools can indicate cancer, kidney failure or liver disease.
A minimal amount of clear nasal discharge is normal. However, increased, thickened or opaque discharge can mean that the nasal passages are infected, or they can indicate an allergic reaction to perfume, pollen, smoke and other airborne impurities. Any trauma or injury to the nose can cause nasal bleeding, which can be treated by applying gentle pressure and with pain medication. Tumors and foreign objects embedded deeper inside the nose cause more bleeding and require medical attention.
Changes in the texture and pigmentation of a dog's nose can signal underlying medical conditions. While some changes are normal for certain breeds as they grow older, significant color changes or excessive peeling and flaking should receive immediate medical attention.