After selecting the shampoo in the player's Supplies menu, the player is shown an interface with the player's pet and a sponge. The player must drag the sponge across the dog to scrub its fur, covering it with bubbles - dirty gray at first, but as the player scrubs, they will turn white. In the 3DS version, the player must make sure to wash both sides of their pet. After that, they must 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 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, the player's dog will become Dirty not only if he or she is 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 participate in a contest if they are Filthy, and on walks, other dog owners passing by may make comments on a dog's cleanliness, although those two aspects do not apply to the 3DS version. In the Obedience Trial, 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.
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, and the player can find both kinds of shampoo on walks. Pets will also occasionally do certain tricks such as sit up, stand up, and cheer in the bath.