Reduce humidity - dehumidifier or open window.

Keeping bathroom humidity below 60% starves mold of the moisture it requires. A dehumidifier or an open window after showering accomplishes this depending on bathroom layout and climate.

Dehumidifier

A compact bathroom dehumidifier pulls moisture from the air continuously. Place it away from direct water spray and empty or drain the reservoir regularly. This option works best in windowless bathrooms or humid climates where outside air provides little relief.

Open Window

Opening a window during and after showering creates cross-ventilation that carries humid air out. This is effective in dry or temperate climates but less useful on hot, humid days when outdoor air is already moisture-laden.

Choosing Between Them

Use a dehumidifier when outdoor humidity regularly exceeds 60% or the bathroom has no window. Use the window method when outdoor air is drier than indoor air. In mild climates, the window approach costs nothing to run.