Install an exhaust fan or a dehumidifier in the bathroom. That’s the easiest solution.

Is there a window in the bathroom? You can keep it open and run the ceiling fan for a while. That should help. Dehumidifiers are usually expensive, but you can have an exhaust fan installed.

Bathrooms need natural air and you have to keep the door open for some part of the day. May be you can do it when you are not using the room. If you don’t have space for exhaust fan, install a ceiling fan, put it on and open the door for a while.