Vapour in between window panes?

I get a little bit of vapour in between the panes of a PVC window (at a corner) when it is very cold outisde (under 20C). I don't see the need to replace since it is not a big problem, my question is: is it going to get worse and can I fix it by caulking? Also, would caulking work with condensation between panes in a double-paned window that is not PVC?
Many thanks...