Sometimes if your dog is sensitive to specific things like dyes, chemicals, or smells that are found in these soaps they can develop a rash which can cause red bumps, sores, and hair loss. If
your vet thinks that the soaps could be the reason then make sure that you or
your groomer is using hypoallergenic shampoo. Usually this means that they will be using a milder oatmeal shampoo, it still smells good but it may cost a little more.
Make sure you visit the vet...
Good luck!