Why is Isopropol alcohol only 91% or lower? And so cheap? And why does it burn, (sting)?

Answer 1

Isopropyl alcohol can be purchased 99% pure, but it is quite expensive at that purity. It should not sting on intact skin, but if there are any openings in the skin, so that the alcohol comes into direct contact with living cells, it rapidly dehydrates those cells by drawing water out through the cell membranes, and the local nerves react to this by sending pain impulses to the brain.

Answer 2

Cause if it burns it means its working