This is a little bit of a chemistry lesson. Sorry, but there is a need to explain a little bit about alcohols in relation to sanitizer. I will keep it brief, I promise!
Alcohol #1 (Methanol) I call methanol "alcohol #1" because it has just one carbon atom. The rest are Hs and Os. The key thing to know about methanol is that it is VERY, VERY poisonous. It is so toxic that consuming a couple of shots of pure methanol would likely be fatal. In your body, methanol is metabolized to formaldehyde and formic acid which can cause blindness and death. It can also be absorbed somewhat through skin contact. Methanol is naturally produced in small amounts during fermentation, but not in amounts that are dangerous. Distilling concentrates all three alcohols we are discussing. Poor distilling practice can lead to methanol levels that are unhealthy, especially with certain feedstocks such as stone fruits. For the record, our sanitizer uses extremely pure neutral spirits that typically have only about a part per million of methanol. It is very safe on your skin.
Alcohol #2 (Ethanol) This is the one that we all know (and some love!). You can probably guess that it has 2 carbons. It is the main product of yeast fermentation of sugar and leads to a delightful array of beverages. For the purposes of sanitizer, the ethanol is highly purified into "neutral spirit" (i.e. no flavor or impurities). At that point, it is 95% ethanol and about 5% water. To make sanitizer, we add hydrogen peroxide, glycerin, bittering agent, and a little water. The high concentration of alcohol, of course, kills bacteria and viruses by de-naturing the proteins of their metabolic machinery. The peroxide is to kill spores. The glycerin is actually to prevent your skin from drying out since the alcohol strips the oils from your skin. As a personal note, I have found that I like the World Health Organization liquid formulation better than the typical gels. The WHO formula moisturizes your hands without leaving a sticky film. The bittering agent is to protect children and those prone to substance abuse by making the sanitizer so terribly bitter that no one will mistake it for something to consume. Finally, a bit of purified water bring the final alcohol concentration to 80%.
Alcohol #3 (Isopropanol or Isopropyl Alcohol) I am also including the 3 carbon alcohol because it is also made into sanitizer. Only a tiny amount is formed by fermentation - most of it is of petrochemical origin. It is also toxic and has a distinct solventy smell. The prefix iso means "equal" and this refers to the fact that the alcohol group is attached to the middle of the three carbons. Iso makes perfectly good sani if you don't mind the smell, but we are sticking with ethanol for ours.