Cupboard under stairs smells really musty

[BlueBloodedBlue]

It doesnt seem to be damp but has an exterior wall and any coats put in there smell awful.

Any ideas as to what we can do please?

I keep door open for air circulation overnight - this has made a massive difference. I also put the little single use dehumidifiers in there. Before I had flooring all redone and sealed there was a hole which led to under the house. This caused a lot of damp.

My understairs cupboard is the same. It’s got an exterior wall too. I just keep bikes in there so nothing gets smelly, but last week I decided to put a dehumidifier box in it and it’s collected a decent amount of water already. I should maybe keep the door open a bit too!

We occasionally get mice in ours. They don't venture anywhere else but maybe you have visitors?