@fortran42,
I've had this problem off and on over many years and haven't really gotten to the bottom of it, but I will say that it has not kept me from hiking thousands of miles (the Pacific Crest Trail, Camino trails in Europe, etc.). However, it is particularly bad right now--following a hike in town (not near any poison oak, etc.) on roadways. It doesn't itch, but I sometimes wonder if there is a possibility that it might become infected.
It's just on the inside of my lower legs--so I think it is the socks, on warm days, plus the friction of legs rubbing against each other. I, too, am going to experiment with wool or synthetic or various other compositions of my socks.