Out of all the places in your home where you are likely to have mold issues, your bathroom is on the top of the list. This is because of all the different sources of moisture that you will find in a bathroom. Whenever you have hot water running, you will have an increase in the humidity in your bathroom, which can then condense in the wrong area and promote mold growth. Another problem is in bathrooms where there is carpet since water that splashes on the floor can sit in the carpet for a long time, presenting fertile ground for mold to grow.
You want to keep an eye on pipes that could be leaking in your bathroom as well. Even just a small drip from a pipe or a sink that has cracks or gaps could collect and lead to mold growth.
It is important that your bathroom has good ventilation, and this means that you should have a ceiling fan that operates properly. Without this, you are fighting a losing battle in your bathroom.