The pink mold that grows in the bathroom is caused by low air circulation, warm environments, poor lighting and high humidity. Pink mold in the bathroom is usually caused by a type of bacterium known as serratia marcescens, which is present in household air. It floats around until it finds a suitable environment in which to grow. Typically, it chooses areas that are warm and moist.
Simply scrubbing the moldy area removes the pink coloring, but not all of the bacteria. This is why the pink color returns after just a few days. One way to clean a shower, for example, is with a solution made up of 1 gallon of water, 2 tablespoons of liquid detergent and 1 cup of chlorine bleach. Once the solution is poured all over the shower, it needs to be scrubbed in and left to dry. After the solution dries, rinse the shower with clean water.
To deter the mold from coming back, the humidity in the bathroom needs to be kept low. This can be done by leaving the bathroom door open for 15 minutes after bathing or by installing a bathroom fan. Mold growth is also inhibited in well-lit areas. The lights do not have to be left on all the time, but leaving them on for a few hours after bathing helps prevent mold growth.