The lack of ventilation is the single most potential problem in your bathroom. This is caused by the moisture build up that happens every time anyone takes a shower. Too much moisture can cause mold, ugly water spots, peeling paint, rust, and drip marks on the ceiling.
Although many people think that opening a window in their bathroom will help, it just won’t do the trick. If it’s too cold outside you will freeze and if it’s too hot, you will let in more moisture.
The best solution is a properly vented fan with a timer. Make sure the ventilation fan runs for at least 20 minutes after the shower. Do not keep the fan on too long, otherwise, it will interfere with your heating and air conditioning.