Mushrooms in Wet Room

Hi, I had a wet room installed about six months ago. I am the only person who showers in but I do use the shower every day. The toilet and basin only get used at night and morning and only really by me. Tonight my husband (glad it wasn’t me) discovered a couple of mushrooms growing behind the door, which he thankfully removed, then he put some bleach down. My house is kept really quite clean and tidy. I can imagine the wetness in the room encouraged the growth of the mushrooms. The wet room was made by borrowing from the bedroom so there is no window in the wet room although the bedroom has a window. Sure this encouraged the mushrooms to grow too. There is an extractor fan which I do use. Just wondered if anyone else had noticed this and if so what they did to keep them away. Thanks Cheryl:-)

Perhaps it would be worth getting a dehumidifier since the extractor fan seems not to be enough?

Do you leave the wet-room door & bedroom window open after a shower, so that fresh air can circulate ?