Thanks a lot everybody for the strong response to my problem.
Now I know this is a common problem and I fixed it with gloves.

The problem number two is that I, however, have 20 assemblies that could
serve in a criminalogy teaching class. Is there any way to clean them? I
tried several substances I had around and Methyl Ethyl Ketone works the
best. Will it damage the board (solder mask, joints, ICs, etc)?

Thanks, Ioan

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