Normal dryness
A dog's nose is kept moist by its own secretions and by licking. After a nap, in a heated room or on a windy walk it will often be dry and warm, and moist again an hour later. That is not a problem and needs nothing.
When the surface changes
A nose that stays dry for days and develops a rough, cracked or crusted surface is a different matter. Common causes are winter air, sun exposure on lightly pigmented noses, some plastic bowls, and age. Some breeds are prone to a thickening of the nose surface. Any of these can be helped by simple care; a few need a vet.
Simple care
Apply a very small amount of a balm made for noses, about the size of a grain of rice, to a clean nose. Do it when the dog is resting, since it will lick most of it off within minutes otherwise. Once a day for a week is usually enough to see the surface soften. Choose a balm made to be licked, with no fragrance and no essential oils.
Sun
Pink or pale noses burn. A dog that spends the summer outdoors may need shade at midday and, if the vet agrees, a pet-safe sun protection on the nose. Human sunscreen is not suitable, because it will be licked off and swallowed.
When to see a vet
Bleeding, sores, loss of pigment, a change in the shape of the nose, a discharge from the nostrils, or crusting that keeps returning despite care. These can point to conditions that need diagnosis rather than a balm.