I bathe mine only when needed. Which is usually about twice a month since they seem to like to crawl through their poo.. sometimes I use just a tiny amount of baby shampoo. But dont get any on their head. They can get a RI if anything gets in their nostrils, pits or mouth. Then just rinse well with luke warm water.
Soap of any kind isnt needed tho. If they are dirty or smelly, just a warm soak and a gentle rub-down (in the direction the scales grow of course) is all you really need to do... I only use a dab of baby shampoo because it helps condition & soften the skin (scales) if they are due to shed soon.