Huge mould patch behind wardrobe

[Blissbiz]

I've found the most disgusting black mould patch behind my wardrobe. It's huge maybe 4ft x 4ft.
The wardrobe was pushed tight to the wall and it's solid on the floor, also the top of the wardrobe had stuff on top pushed on the wall. I've cleaned it with dettol mould removal and I can't believe it has come off. But what do I do now?I can't believe I didn't smell it, the humidity is 70% in the room which I think is quite high? I've ordered a dehumidifier, currently airing it out with windows open and obviously haven't pushed it back to the wall. My dd has had a cough for the last few weeks and most nights she sleeps with me I feel terrible. Will this of caused the cough and if the mould has gone should the cough go too? Any advice to get rid of mould/bleach smell would be good too

Useful thread, thank you all.

Our problem with condensation and mould in my daughter's room vanished as soon as I started leaving the window open a crack every night.

water vapour is lighter than air and, undisturbed in a steamy bathroom, rises towards the ceiling where the extractor sucks it outside. Cool, dry air enters under the bathroom door and forms a layer under the hot, damp air.

Opening the door or windowe stirs the air up and prevents stratification. Worse, it prevents the fan generating suction in the room, and allows the steam to diffuse into the house. Depending on wind direction, air entering through the window can push the steam into the house.