If you live in an environment that is warm, there is a possibility that a mold would grow on the walls. These molds are a kind of fungus and they could be extremely harmful for the walls. They should be removed immediately. The bathroom is the area that is affected worst by the molds. In order to remove the molds from the walls, you will have to reduce the humidity of the house. The fan of the bathroom ahs to turned on. The moisture will be pulled from the air in this way and the humidity could be kept under control.
You can keep the window of the bathroom open for a few hours a day so that the circulation of air is improved. Molds are likely to grow less on areas that are well lit. Therefore, you will have to keep the lights on for a few hours each day. The growths of the molds are nourished by scum of soap and body oil. You should clean the bathroom regularly.