1. Nails should have not suffered. It is the bacteria and viruses that degrade the DNA inside the nail's structure, not the voltage across them.
2. Too much is a relative term. The nails should work for some time, but it is difficult to know how rapid the damage happens, or when one would need to replace the nails that have been treated with the higher voltage. There aren't good tools to measure the damage or the amount of signal received by the target cells.
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