Why can my body conduct electricity from a 9 volt battery?
Current depends on voltage and resistance.  Look up "Ohm's law"

E=IR

Where E is voltage in volts, I is current in amperes, and R is resistance in ohms.

Using 5V and assuming a reasonable  value for skin resistance of 10000 ohms  you get 0.5 milliamperes of current.

An efficient LED can produce visible light levels with that amount of current.

Your skin resistance varies depending on many factors.  It is lower when you sweat and higher when your skin is dry.

This makes it difficult to guess how much current is really flowing, but obviously some current is getting through.



It isn't hurting you because the current is very low.  It takes a lot more current, and it has to pass through your heart, to kill you.

I have been plugged into 110VAC, and I am still here.  I do not recommend you try it.  It hurts like hell, and can kill you.  I got lucky.  My brother (who accidentally zapped me) noticed quickly enough and unplugged the cable I had been working on.  It is certain that I could not have let go on my own, and would have eventually died if it had gone on longer.