The colour of a dog's nose depends on its colouration and its colour genetics: dogs with dark pigment have black noses, regardless of their coat colour. Dogs that naturally have mixed flesh colour and black pigment can have either "butterfly" or "Dudley" noses. However, the pigment of a dog's nose can even be affected by the environment or illness.
Black Noses and "Self-Colored" Noses
Dogs frequently have genes for normal skin pigment: BB or Bb (black) or bb (brown). Although dogs with brown noses cannot support black pigment, the chocolate dog has "normal" pigment intensity. By contrast, dogs with dilute skin pigment (dd) have a blue-grey "self" coloured nose. Because of the way that the dilute "blue" gene works, however, the dilution may take place "over" the normal black pigmentation, in a manner very similar to the genetics that go into making red hair in human beings. This process may lead to the belief that dog with an apparently black nose has a nose that is lightening when it takes on a blue sheen under light.
Puppies are born with unpigmented noses. Over the first two weeks of life, the nose is "filled in" with spots of black, brown or blue pigment until it reaches the colour the puppy will have in maturity.
According to the American Kennel Club Glossary, a "butterfly" nose is one that is "partially unpigmented. . . dark, spotted with flesh colour" because the process of filling in was never completed. This colouration is primarily dark and covered with pigment except for gaps between the spots of pigment that were never filled in. As the puppy grows to maturity, these gaps may become more noticeable, leading to the misconception that the dog's nose is lightening.
Vitiligo and Autoimmune Disease
According to DoggedHealth.com, vitiligo is "purely a cosmetic concern [that] tends to impact certain breeds more than others." Vitiligo is not a condition that is restricted to the area of the nose; it can also affect the lips, eye rims and lips. A "Dudley" nose, defined by the American Kennel Club as a "flesh-colored" nose, is an expression of vitiligo.
In addition to vitiligo, dogs may be affected by an autoimmune disease called discoid lupus erythematosus (DLE), which causes raw patches and pigment loss on the nose, among other symptoms. Even though DLE is treatable, it is not curable. Treatment might need to continue for the dog's entire life; however, with treatment, the pigment might return to the tissues.
"Snow" or "Winter" Nose
The American Kennel Club Glossary defines a "snow nose" as one that is "normally solid black but acquires [a] pink streak in winter." This kind of pigmentation loss typically occurs in arctic (Northern) breeds, such as huskies, malamutes and related breeds. Although snow nose typically reverses itself with the advent of warmer weather, it may be permanent in some dogs.
Plastic Dish Dermatitis
Some dogs have an allergic reaction to plastic, particularly plastic dishes that release a chemical when chewed or damaged. According to VetInfo.com, this kind of lightening might be easily treated simply by replacing the plastic bowl with a ceramic one. However, certain dogs might not recover from this kind of depigmentation.
Healing flesh on a dog's nose from a cut or a bite, for example, typically comes in pink and gradually darkens to the colour of its normal pigment. According to VetInfo.com, topical ointments can be used to treat this kind of wound. However, a dog that has experienced a burn from chemicals, heat, sun exposure or electricity will also experience lightening of the nose pigment. According to DoggedHealth.com, this kind of trauma results in permanent lightening of the tissues.