During the French polishing of the last three or four of my guitars, I've had the skin on my fingers eventually slough off and peel away to leave tender new skin. After the first time it happened, I tried protecting my hands with latex gloves, then vinyl, and then nitrile gloves, all to no avail.
I was puzzled because this hadn't happened to me in the previous 4-5 years of French polishing guitars. Thinking back over it, the only thing that changed was my vendor for denatured alcohol. I originally had used some product from a local paint shop that was ~95% ethanol and the rest methanol. My problems began when that shop closed and I switched to the Ace Hardware product. I looked up the MSDS online and found out that it only has ~45% ethanol but has a whopping 45% or so of methanol. I was shocked and dismayed. Okay, ;and felt a little stupic.
So, for the latest guitar, I used some Hock denatured alcohol that I bought at Woodcraft. It has 98% ethanol and only 2% methanol and I had absolutely no problems with skin peeling, etc.
Lesson: beware of gross methanol exposure and know what you're drinking.