Maureen, you have a maintenance caused leading to mold and mildew that is created by normal usage. More than likely the cause of this is a lack of ventilation in the bath or non use of ventilation. Do you have a window installed in the bath and if so, it should be opened a crack during shower/bath time and open when the weather is nice. Is there a fan in the bathroom ceiling? Is it working? And is the fan venting to the outside? The moisture from your shower and bath does not have a way to be removed from the hot steamy bath area, if you do not have a window and/or a working fan vented to the outside. Commonly you should leave your fan on several minutes after the shower/bath. and more importantly if you do have these items, they must used. These issues should really be addressed as the mold/mildew will just continue to grow and create additional issues and they could become more severe over time. The EPA has simple guidelines to remove and clean these types of mold/mildew issues. Typically it is soap and water and here is the web link www.epa.gov/mold/.