Unless you want to grow these......
in your bathroom, remember to install one of these.
These are quiet, require a 6" duct (you'll probably have to change it out from a 4" duct), can operate on a timer, and suck all the humidity out of the room after a nice, steamy, hot shower.
They're worth it.
These fans have all kinds of options and need to be sized to fit the room and your needs. When you remodel, change that builder fan out.
No money exchanged hands for this endorsement. :)