Hand sanitizers provide a convenient and effective way to clean your hands if soap and water aren't available and your hands aren't covered in visible dirt or grease. According to a 2019 ruling by the FDA, a product can be marketed as a hand sanitizer if it contains ethyl alcohol (also called ethanol), isopropyl alcohol (isopropanol) or benzalkonium chloride as the active ingredient.
The key ingredient in most hand sanitizers is alcohol. Chemically speaking, alcohols are organic molecules made of carbon, oxygen and hydrogen. Ethanol is the chemical in alcoholic drinks and is the chemical most people are thinking of when they say alcohol. Propanol and isopropanol (isopropyl alcohol) are two other alcohols that are common in disinfectants because they're highly soluble in water, just like ethanol.
Alcohols destroy disease-causing agents, or pathogens, by breaking apart proteins, splitting cells into pieces or messing with a cell's metabolism, according to a 2014 review published in the journal Clinical Microbiology Reviews. Solutions with as little as 30% alcohol have some pathogen-killing ability, and the effectiveness increases with increasing alcohol concentration. Studies have shown that alcohol kills a more broad variety of bacteria and viruses when the concentration exceeds 60%, and it works faster as the concentration increases. But the effectiveness of alcohol seems to top out at about a 90-95% concentration.
Another strength of alcohol is that the bacteria it kills don't develop a resistance to it, so alcohol doesn't lose effectiveness with continued use.
According to the 2014 review, ethanol is so powerful that a few studies have found that in high concentrations, it's better at getting rid of three species of disease-causing bacteria — Escherichia coli, Serratia marcescens and Staphylococcus saprophyticus — compared with washing hands with regular or antibacterial soap.
But alcohol doesn't work for all germs, such as norovirus; Clostridium difficile, which can cause life-threatening diarrhea; or Cryptosporidium, a parasite that causes a diarrheal disease called cryptosporidiosis, the Centers for Disease Control and Prevention says. Hand sanitizers also don't remove harmful chemicals like pesticides or heavy metals, nor does hand sanitizer work well on especially dirty or greasy hands. So, soap and water still win the contest overall.
There are a few small-scale studies demonstrating that an alcohol-free hand sanitizer containing benzalkonium chloride as the active ingredient, at a concentration of 0.13%, is just as effective and even more effective than alcohol at getting rid of bacteria. The alcohol-free hand sanitizer that was tested was called HandClens, and the scientists who conducted the research on it worked for the now-closed laboratory that developed the product. That doesn't mean benzalkonium chloride isn't effective, but there doesn't seem to be independent research to suggest that it's better than alcohol. Plus, benzalkonium chloride might be harmful for some individuals, especially at higher concentrations, according to the Hazardous Substances Database.
According to the CDC, hand sanitizer without alcohol may not kill as many germs and may only reduce the growth of germs rather than killing them outright. The CDC recommends hand sanitizers with at least 60% alcohol in them for maximum effectiveness.