Most hand sanitizers are built around one core ingredient: alcohol, typically ethanol or isopropanol, at a concentration between 60% and 95%. Everything else in the bottle serves a supporting role, from keeping your skin moisturized to giving the product its gel-like texture. The formula is simpler than you might expect, but each ingredient has a specific job.
The Active Ingredient: Alcohol
Alcohol is what actually kills germs. The two types used in hand sanitizers are ethanol (the same type of alcohol in beverages, though rendered undrinkable) and isopropyl alcohol, sometimes called rubbing alcohol. The CDC recommends using a sanitizer with at least 60% alcohol, and concentrations between 60% and 95% are the most effective at killing germs.
Alcohol works by denaturing proteins, essentially unraveling the molecular structures that bacteria and viruses need to function. Interestingly, pure alcohol is actually less effective than alcohol mixed with water. Water helps the alcohol penetrate microbial cells, which is why hand sanitizers aren’t made with 100% alcohol. At effective concentrations, alcohol inactivates all viruses with a lipid (fatty) envelope, including influenza and herpes viruses, along with many non-enveloped viruses like rhinovirus and rotavirus.
The World Health Organization publishes two standard formulations for hand sanitizer production. The first uses ethanol at a final concentration of 80%. The second uses isopropyl alcohol at 75%. Both are proven effective, though ethanol-based formulas have a slight edge against a broader range of viruses. Isopropyl alcohol is fully active against enveloped viruses but less effective against some non-enveloped types like enteroviruses.
Why Sanitizers Contain Hydrogen Peroxide
Both WHO formulations include a tiny amount of hydrogen peroxide, just 0.125% in the final product. This surprises many people because hydrogen peroxide is a well-known disinfectant on its own. But at this low concentration, it isn’t there to disinfect your hands. Its job is to kill bacterial spores that may have contaminated the sanitizer during manufacturing. It’s a quality control ingredient, not an antiseptic one.
Glycerin and Other Moisturizers
Alcohol is harsh on skin. It strips away natural oils, and frequent use can cause dryness, cracking, and irritant contact dermatitis. That’s why virtually every hand sanitizer includes at least one moisturizing agent.
Glycerin is the most common. In the WHO formulations, it’s present at 1.45%, and studies show it promotes skin hydration in proportion to how much is used. Glycerin is a humectant, meaning it draws water from the environment and deeper skin layers to the surface, keeping the outer layer of skin from drying out. Some commercial products go further, adding propylene glycol (another humectant), aloe vera extract, or vitamin E to improve the feel on skin and reduce irritation from repeated use. These ingredients don’t affect germ-killing ability. They’re purely there for skin comfort.
What Makes It a Gel
Liquid hand sanitizer would run through your fingers before you could rub it in, so manufacturers add thickening agents to create the familiar gel texture. The most widely used thickener is carbomer, a polymer that gives sanitizer its slightly thick, transparent appearance. Carbomer has a useful property: it stays firm when sitting in the bottle but becomes fluid the moment you rub your hands together. This shear-thinning behavior means the product holds its shape when dispensed but spreads easily across your skin under friction. Some formulations use cellulose-based thickeners instead, but carbomer is preferred for its clarity, stability, and smooth feel.
Denaturants: Making Alcohol Undrinkable
Because ethanol-based sanitizers contain drinkable-grade alcohol, regulations require manufacturers to add denaturants, substances that make the alcohol taste terrible or cause nausea if swallowed. The most common denaturant is denatonium benzoate, one of the most bitter substances known. Only a tiny amount is needed. Other approved denaturants include tert-butyl alcohol and various chemical additives, all regulated by the U.S. Alcohol and Tobacco Tax and Trade Bureau. These compounds exist solely to prevent misuse and are present in quantities too small to affect the sanitizer’s performance.
Alcohol-Free Sanitizers
Not all hand sanitizers use alcohol. The most common alcohol-free alternative relies on benzalkonium chloride (BKC), a type of quaternary ammonium compound. It works differently from alcohol: instead of denaturing proteins, BKC is a positively charged surfactant that binds to the negatively charged membranes of bacteria, disrupting their structural integrity. It also breaks apart the lipid envelopes of certain viruses.
Commercial alcohol-free sanitizers typically contain BKC at concentrations between 0.1% and 0.13%. Both the U.S. Environmental Protection Agency and Health Canada have approved BKC as effective against SARS-CoV-2 at concentrations of 0.1% to 0.15%. However, the CDC notes that alcohol-based sanitizers are generally more effective at killing a broader range of germs. Alcohol-free options are useful for people with skin conditions aggravated by alcohol or in settings where flammability is a concern.
Contaminants to Watch For
During 2020 and 2021, the FDA issued warnings about hand sanitizers contaminated with methanol (wood alcohol), a toxic substance that can cause blindness, organ damage, and death if absorbed through the skin or accidentally ingested. Methanol is not a legitimate ingredient in hand sanitizer. It appeared in certain imported products that used impure alcohol sources or substituted methanol for ethanol to cut costs. The FDA maintains a searchable list of recalled products. If your sanitizer doesn’t clearly list ethanol or isopropyl alcohol as its active ingredient, or comes from an unfamiliar brand, checking that list is worth the 30 seconds.
Shelf Life and Storage
Hand sanitizers are regulated as over-the-counter drugs by the FDA and are required to carry an expiration date. The main concern with expired sanitizer isn’t that it becomes harmful but that alcohol gradually evaporates over time, potentially dropping the concentration below the 60% threshold where it’s effective. This happens faster when the container is only partially full or has been stored somewhere warm, like the interior of a car. An expired sanitizer still has some germ-killing ability, but you can’t be sure it meets the minimum effective concentration.
For maximum shelf life, store sanitizer in a cool location with the cap tightly closed. Most products remain effective for two to three years from the manufacture date when stored properly.