I'm interested to know if you find any answers!

My teenage son has had some cracking, peeling skin issues on his soles. It started this summer. He has peeling between the toes and on the ball of his foot, but no redness or soreness. It really does not seem to be fungal (we know what that looks and feels like). It's not itchy. Just keeps peeling, cleanly, like a sunburn might. Also the skin is very thick on his soles, even though he NEVER goes barefoot or even wears sandals. He once said his feet feel like they have plastic on the bottoms. The skin feels like vinyl. It cracks and forms fissures especially under his big toe. It helps to put Eucerin cream on them once a day. He also had a toenail that fell off some time ago. It has grown in again, but the nail is mottled, and a few of his nails have some pitting.

His Dr. didn't know. Very frustrating.

In this case it does sound like an infection, most likely fungal.  I recommend treating it like a fungal infection just in case.  Soaking his feet in a strong black walnut hull tea several times a day is a good start.  He should always put on clean sock afterward.  And don't forget to sterilize the shoes.  This can be done by spraying the shoes inside really well with Lysol, then placing them in a plastic bag for a while to allow the Lysol to permeate the shoes completely.

A deficiency of B vitamins can also lead to cracks in the skin, so foods high in B vitamins or a B supplement would also be a good idea.