Eli5 How does hand sanitiser kill bacteria?
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Hand sanitizers contain different disinfectants, but usually is some sort of alcohol. How it works is that bacteria have a cell membrane like their “skin” around them, which is composed of lipids, which are essentially fats. As you know that oils and water don’t mix, in the same way a bacteria’s membrane stays intact. But when there is alcohol, these can bind to both the oily molecules of the bacteria’s membrane, as well as water. Essentially now, oil can dissolve in water with the help of the alcohols. The bacteria’s membrane breaks apart and dissolves away, and the insides of the bacteria spills out and bacteria dies. Soaps behave in similar ways as well.
Another aspect is the fact that alcohols can denature proteins. A bacteria’s membrane doesnt only contain lipid fats, but also contains proteins as well. In order for proteins to behave properly they are folded in very complex, and specific ways. Proteins can easily become denatured for various reasons, including heat and chemicals. Alcohol causes the proteins to unfold and become useless, and even weaken the bacteria’s membrane. This also contributes to the bacteria breaking up and the inside spilling out and dies.
Now you may be wondering, then why doesn’t this happen to human skin? After all, our skin cells are also surrounded by cell membrane. Although it does damage our skin, but because we have the outer layers of skin is dead skin cell layers, so when we use hand sanitizer we are protected a bit.
Some hand sanitizers contain triclosan. The US has banned triclosan, but similar chemicals are used sometimes. How these chemicals work is because bacteria and some fungi make the fatty chains of their cell membranes by several enzymes. Triclosan and similar chemicals bind to these enzymes, making fatty chain production impossible, and thus the bacteria is unable to create, repair, and maintain its membrane, and eventually will die. Humans are not affected by triclosan and similar chemicals because we don’t use the same enzyme for fatty chain production, and thus are unaffected.
Bacteria cell membranes, the ‘bag’ that holds all the parts in, is made of a layer composed of fat molecules. Since hand sanitiser typically contains alcohol or another similar solvent, it can literally dissolve the bacteria and its parts will spill out. Soaps also do the same thing, because they’re chemically similar to the membrane fats – however they tend to mix with them instead and this stops the bacteria from functioning properly.
Most hand sanitizers contain a huge amount of various forms of alcohol, like 60% alcohol. Alcohol can basically *melt* the outer membranes of bacteria which kills them. Some hand sanitizers might contain other ingredients, and may/may not work, but the tried and true method is melting bacteria skins with concentrated alcohol.
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