Yeah, I'd say it's something like a dermatitis brought on by the fragrance oils? Scent is usually the first suspect in these cases or some odd ingredient, maybe look for a common ingredient if it happens with other soaps? Could it be a sort of allergic reaction(contact dermatitis) to Lanolin rather? Typed this out earlier, swore I thought I had read something about Tallow once not Lanolin, losing my mind.You mentioned Lanolin, and you crossed that out so? The Lanolin reaction is pretty rare at that even. Yeah, Tallow is usually something that heals dryness and redness, used to help with eczema...
Luckily, tallow and lanolin are awesome on my skin.
It's always the scents that irritate my skin or cause migraines, especially the strongly scented artisan soaps.
I had such a horrible run with them a couple of years back (70% strike rate!), that I just stopped buying them at all!
Now I have around 8 soaps that are mildly scented but mostly just use my own unscented shaving soap loaded with butters.