The Best Value For Carpet,Tile & Air Duct Cleaning!
Replace the grout between bathroom tiles every three to five years. If your grout is intact but dirty, or has mold and mildew growing on it, you may be able to clean it instead of replacing it. It is a good idea to try milder products for grout cleaning first and only resort to harsher chemicals if the milder ones do not get your grout clean. Repeated use of harsh chemicals breaks down grout, and then you will definitely need to replace it.
Use mild household products first to remove mildew and clean grout.
Read more at: http://www.wikihow.com/Clean-Bathroom-Grout