Hi …
I’m sure this is a easy one… but since I’m new to ZBRUSH I have no clue 
How can I get this bubble out of the mesh? Smoothing does not seem to work… since it also reduces the since of the mesh.
Any ideas?
hi,
have a look at the retopology tutorials for how to proceed … good luck ! 
Your topology is causing those bumps. Check out this vid for a scientific explimication…
http://www.guerrillacg.org/home/3d-polygon-modeling/subdivision-topology-artifacts
Try to not redirect the topology so much. Zac Petroc’s Gnomon DVD has a good tutorial for building a basemesh. Gnomon also offers a free mesh by Alex Alvarez on the workshop site.
Hold down shift+LMB, start smoothing, let go of shift NOT LMB, and continue smoothing. This should work, it has worked for me.