What voltage/amperage would be needed to feel a sensation when the current is applied on the human skin?

What voltage/amperage would be needed to feel a sensation when the current is applied on the human skin? 

It is pretty safe to say that 1mA will be felt just about anywhere on your body.

I did some testing years ago, I made my own apparatus with a current limited high voltage. The voltage was applied to two points about 2cm apart to avoid having the current pass through anywhere dangerous.

I didn't probe everywhere... Just my hands, arms, and chest. The most sensitive was between my fingers. I could just barely feel 300uA. By 1mA, I found it very uncomfortable. But on other parts of my hands, arms, and chest, it took close to 1mA to feel it, but became very uncomfortable under 5mA.

But it takes voltage to push current. Your tongue is a decent conductor. I find that to test a 1.5V battery, I have to use my little finger and lick the tip of it before applying it to the negative side of the cell, or I can't "taste" a good 1.5V battery.

I did a lot of resistance readings and calculations. Skin is a huge variable. It can be hundreds of thousands of ohms or even millions. But it could drop to a few hundred ohms. The flesh underneath is only a few hundred ohms give or take depending on if it is muscle or fat.

It has been a very long time since I did my tests, and I've since lost the notebook with the results. I do recall calculating that if you were to puncture the skin in two places, a 5V power supply could give you a bad shock, although not likely to be lethal. But that a 12V power supply or battery could possibly be lethal.

If you penetrate the chest or head, of course, it may take much, much less. Only a few microamps (millionths of an ampere) can be enough to cause your heart to fibrillate. Fortunately, it is set between your air filled lungs, deep in your chest.

Generally, if you don't puncture the skin, 30V has a good possibility of causing sensation, and 50 or 60V is almost certainly going to give you a shock that you can feel. The voltage is generally considered to start being dangerous around 50 or 60V. Sweaty skin is lower resistance than merely wetted skin, or dry skin. Hair will reduce the surface area in contact and increase resistance.

There are outliers, of course. I've known people with skin so dry that they can touch 120Vac house wiring and not feel it. I'd never do that! What if that day you had a paper cut or a little salt on your skin from breakfast?