I was looking at all of this really close a while back because I was trying to find some locally in my area - I came across USP Glycerin in CVS - It did say NOT for internal - external use only - BUT a pharmacist on board here replied to the thread and stated the it's ALL mfr'd by Humco labs - and it was all the same - I've been using it for over a month now and it works perfect with NO side effects at all - I did see the Wiltons at Michael's and other than the label - it looked IDENTICAL - you'd be surprised at how many name brand pharmaceutical mfr's make both the brand and the generic - both are exactly identical, but called different names ! I was in the wholesale pharmaceutical business for years and I've seen that first hand - the generic would cost $1.25 and the brand would cost $10.25 and they were both identical, but you'd have a hard time trying to convince someone of that who was hung up on name brands.
Just my .02 worth !
I use the glycerin from walmart. 99.5% glycerin .5% water. I contacted Humco and they told me it was vegetable based, and yes from what I have heard Humco manufactures all the glycerin sold in the U.S. It is then bought in bulk by other companies and they just put their own label on it.