After selecting the shampoo in the player's Supplies menu, the player is shown an interface with the player's pet and a sponge. Drag the sponge across the dog to scrub its fur and it will become covered in bubbles - dirty gray at first, but as the player scrubs, they will turn white. In the 3DS version, make sure to wash both sides of your pet. After that, tap the shower icon and move the showerhead around, spraying water on the pet and rinsing the shampoo off. When the bubbles are gone the dog should be squeaky clean and sparkling.
In the 3DS version, pets will occasionally do certain tricks like sit up, stand up, and cheer in the bath. Nobody really knows why they do this, but there is a theory going around that they want to show off or want bubbles on their bellies!
In the DS version, players can view how clean their dog is by tapping their dog's name in the home menu. There are five different levels of cleanliness: Beautiful, Clean, Normal, Dirty, and Filthy. Players should not let their dogs get below Normal level. Unlike the 3DS version, dogs will only get Dirty and Filthy if left for a period of time without washing. Over time, the dog's cleanliness will gradually decrease until they are Filthy. But, in the 3DS version of Nintendogs, your dog will become dirty not only if he or she's not bathed often, but also if he or she played in a puddle or ate garbage on a walk. Dogs that are Filthy will have flecks of dirt and fleas hovering around them. Players should bathe their dogs when they are Normal or lower, or when they are Clean or lower before a contest. In the DS version, dogs cannot do a contest if they are Filthy, and on walks, other dog owners passing by may make comments on your dog's cleanliness, although those two things do not apply to the 3DS version, and for Obedience trials, one point is earned to a dog's final score if they are Beautiful. Players should brush their dogs immediately after bathing them, for the best result. When a dog has just been bathed and brushed, he or she will walk back into the house and will sparkle for about 1 minute.
In the 3DS version, both dogs and cats can be bathed. Shampoo comes in two types: normal (which can be bought at the BARC store for $3) and Premium (which can be bought at the BARC store for $6). Both can be used for any short-haired and long-haired dogs/cats. You can also find both kinds of shampoo on walks when you wash your dog the soap is dirty then it turns white.