Some baby shampoos like the traditional Johnsons actually have a high Ph that can dry skin.
WEN is a great all natural shampoo. I use the Yorkies Splash and Shine products. There are other good all natural shampoos and conditioner out there that work well. Most regular shampoos have sulfates that will dry the skin if used regularly. You have to really read the labels carefully because some will say that they have a natural product in them but actually it is a sulfate product with one natural ingredient in it.
All natural products act differently than most sulfate products. They don't lather as much usually but you don't needs tons of bubbles to get your pet clean. As long as you get the product down to the skin and throughout the fur you will have a clean shiny baby when you are done.
Yorkie Splash and Yorkie Shine | Yorkie Shampoo and Yorkie Conditioner
This stuff smell great for days and the hair really shines.