This is a specific difference between the Arctic (or even Alberta where I grew up) and here. There are a lot of other damp places in Canada so I'm sure what's going on here happens in places like BC or even Ontario.
Because of not having central heating and only single pane windows, the house gets quite damp in the winter. You wake up in the mornings with most windows fogged over and if you're not careful mould/mildew will start to grow on outside walls and around the windows (the mystery over why the carpet along the walls in the spare room are bleached has been solved).
I've spent the morning scrubbing the bathroom, the windowsills and I've taken the pull-down shades off the windows, sprayed them and have hung them outside.
Living in the Arctic, you would have to purposefully try to grow any sort of mould. You were more likely to find dust (oh the dust!) and cobwebs around your windowsills if you neglected your cleaning. Here, you only have to go a week or two without wiping the windows down and you'll have a lovely science experiment right in your house.
I think I'd gladly take all the other frustrations of expat life over worrying about if there's mould lurking behind the curtains when I open them.
(Sorry, no pictures in this post. I don't think anyone wants to see any pictures of me cleaning!)