Dogs like Labrador retrievers have been bread to work in the water. Their skin produces oils that help to keep them warm and dry. When you try to give your lab a bath you will notice that the water seems to roll off instead of soak in.

Excessive washing will remove these oils and cause your Labrador's skin to dry out.

Someone could tell you to stick to one bath a month or something similar. Though the only good answer is to only bathe your Lab when he/she really needs it.