Intriguingly, 70% alcohol is a more effective antiseptic than 100% alcohol. Because alcohol causes protein to coagulate on contact, a 100% solution coming into contact with a microorganism creates a hardened protein wall around the outside of the organism, rather than permeating into its interior. Because microorganisms can be very resilient, this protein shell only causes dormancy rather than death. This can lead to revival and a continuation the cycle of reproduction under the right circumstances. At a purity of 70%, however, the alcohol causes coagulation to occur more gradually, slowing down the microorganism from the inside out.
Human skin cells are more resistant to alcoholic coagulation than most microorganisms. This is why your skin doesn't coagulate if it comes into contact with alcohol. Alcohol is also a good solvent that dissolves and carries away non-organic impurities that are responsible for things like odor. Its antiseptic action does cause a burning sensation on open flesh, as anyone who has ever used alcohol to clean a wound can testify.
Alcohol is an ideal antiseptic because it achieves its goal subtly through coagulation, rather than through some active means like active poisoning or dissolving. Throwing acid on an open wound would only be successful at removing the contaminating microorganisms at the expense of a decent chunk of flesh. Ethyl alcohol should never be confused with methyl alcohol, also known as methanol or wood alcohol. Methyl alcohol is used in industry as a solvent, and should never be used for any medical reason. Even small quantities can cause blindness or paralysis, and large quantities can be fatal.
