Guinea pigs ONLY need to be bathed if their fur is caked with urine, grease (e.g., from grease gland), or other substance.
Do not, under any circumstances, submerge a guinea pig when bathing and do not get water in the guinea pig's ears. Hold onto the guinea pig when bathing and
wet only the area that needs to be bathed with warm water. In many cases where a bath is necessary, you may only need to bathe the back end of the guinea pig.
You may consider putting water in a small bowl, putting your guinea pig’s butt in the water, and propping your guinea pigs front legs on the rim so the guinea pig doesn't get any wetter than necessary.
You may also consider using a sponge bath using a damp cloth to clean the dirt area.
Use Gorgeous Guineas shampoo or a gentle baby shampoo.
Rinse and dry thoroughly to avoid chills before returning the guinea pig to his/her home. You may use a hair dryer set to COOL ONLY to help dry your guinea pig.
Long fur does not necessitate bathing. However, long-fur requires daily brushing and regular trimming around the guinea pig's skirt (the fur near the rear end)
to keep it from getting caked with urine and other material.