If I haven't been working with any chemicals recently I'll just rinse well before.
If I've been messing with any test kit chemicals, or anything in the garage (cleaning liquids, gasoline, etc.) then I'll wash and rinse good with bar soap first.
I once made a bad mistake of not washing my hands after testing my tanks.
Within 10 minutes of sticking my hands in the tank, the tank crashed hard, and I lost half my critters before I could do enough emergency water changes to do any good.
Some lessons get learned the hard way...
"Damsels are the yapping, ankle-biting chihuahuas of the ocean.
They have no concept of just how small and annoying they really are."