I seem to have read in a couple of places, that the 'Use by date' is determined by the UBD of the oils that are used to make the soap. (No, I don't remember where - I'm an old man!) But doesn't the saponification process change the oils into something different? I note that soaps are made with all sorts of liquids e.g. milk. Which should mean that the soap is unusable after a couple of days, even before it's turned into soap. The reason I bring this up is because my youngest daughter looked at all my bars of soap, that I've packed in shrink bags with a label attached stating what the ingrediants the soap contains. She said "Dad, you have to write the expiration date on there as well. People who are interested in natural products will want to know!" And I am thinking "How long will it take for beef tallow or coconut milk to turn into something unspeakable?" A bar of soap should be at least a couple og months old before being used. Right??