Snow nose is most often a temporary loss of pigment in the center of the nose. A pink to brown light stripe appears in the center of the nose, with the edges remaining black. The nose returns to full black color during the longer daylight months. Once thought to be a winter-only condition, dogs in warmer southern climates have also been reported to have snow nose. As dogs age, the snow nose may stay around all year long.
The cause is not completely understood. Snow nose is more common in light and white-coated breeds. This condition by itself isn't a health problem, but caution is advised in sunny weather, as the depigmented area is at increased risk for getting sunburned. Some vets advise testing the thyroid levels to make sure that there isn't an underlying thyroid problem.
Other things to consider
Other conditions will cause a loss of pigmentation on a dog's nose. If your dog uses plastic food and water bowls, for instance, a change in nose color may be a reaction to the plastic. Try switching to glass, ceramic or stainless steel bowls.
Thankfully, snow nose is not a health concern, but any changes in your dog's nose — including crusts, sores, discharge, sneezing or wheezing — should be checked as soon as possible by your veterinarian, as the discoloration can indicate serious disease.