Your bathroom is at risk from moisture! Everytime you take a shower, a large amount of moisture is released into the air, and it can lead to all kinds of moisture related problems. One of the most common issues is that of mold, which loves a warm, humid bathroom. Some bathrooms have terrible ventilation, and the only solution might be to hire someone to fix the problem.
A major component in the ventilation of your bathroom is the ceiling fan that moves air out of the bathroom through a duct. However, not all bathroom fans are installed correctly. Some will just vent the moisture laden air into the attic above. This will just move the problem to a different location, leading to mold growth in the attic instead. Some have ducts that aren’t straight, thus restricting airflow. If your fan makes a lot of noise when it runs, it might be time to replace it. You can try to improve things by cleaning the fan out really well, but make sure that you disconnect it from its power source first, since you could run the risk of electrocuting yourself if there are exposed wires.