After each use, you should rinse your natural loofah thoroughly with soap and leave to dry.
Your loofah sponge should be really clean and dry before you put it away.
Wash it occasionally in the washing machine at 60 degrees, do not use fabric softener and put the natural sponge in a laundry bag.
If you have a microwave, put the sponge in for half a minute from time to time to kill the bacteria.
If your loofah product smells bad even after cleaning or if it falls apart, simply dispose of it in the compost.