Lifted some skirting ahead of a reskim to find a damp patch on what I think is the wooden frame of a stud wall. The floorboard immediately 'below' the obvious damp patch is also slightly damp, but it hasn't spread any further than is visible on the photo. There's no other moisture visible, either on the rest of the visible portion of the stud frame or the floorboards along the length of the hallway.
At a bit of a loss as to what the issue might be - the only thing I can think of is an exceptionally slow leaking pipe, but surely that would have caused much more damage by now (talking many, many years without realising this was an issue)?
Could it be a historical issue that just hasn't dried out because its had skirting tight to it? Obviously I'm worried as the impacted wood is very soft.
I suppose a plumber(?) is the best way to go, but I'm really confused as to why if there is an leak it's managed to confine itself to this relatively small area? Any thoughts?