Funnily enough thinking about it I can identify sometimes with the itchy feet thing - sometimes it does seem to be connected to the washing powder, leechates, etc. Another thing I've noticed strangely enough that can bring it on is when your feet have been cold & immersed & then they are drying out afterwards. Thinking about it as well I also find it can occur when the circulation is restricted - eg when I am wearing climbing shoes & then take them off & put my walk in shoes & socks on.