“Protects for hours”: what persistent-activity sanitizer claims really mean

“Kills germs for up to 24 hours.” “Long-lasting protection.” “Resists wash-off.” These claims turn a squirt of sanitizer into an invisible shield, and they sell. The science behind them is real but narrow, the testing is demanding, and in Canada the claim isn’t something a company can just print. Here’s what persistent activity means, how it’s measured, and where the honest limits are.

Two different jobs: killing now versus keeping killing

Every hand antiseptic does one job: reduce the germs on your hands at the moment you use it. Alcohol does this quickly and then evaporates, taking its effect with it. Health Canada’s antiseptic guidance expects a leave-on product to show its effect within 30 seconds.

Persistent activity is a second, separate job. Health Canada’s guidance document on human-use antiseptic drugs defines it as a reduction in skin flora that maintains an extended and low microbial release from the skin, due to slow regrowth of the resident microflora. In plain words: after the product dries, something stays on the skin and keeps the bacteria that live there from bouncing back to their normal numbers.

Immediate kill and persistence are measured separately, and a product can have one without the other. Alcohol alone has almost no persistence. Ingredients that leave a residue, such as chlorhexidine or the quaternary ammonium compounds used in alcohol-free sanitizers, are the ones that make persistence claims possible.

How persistence is tested

Persistence isn’t measured by watching a bottle in a lab; it’s measured on people’s hands. The methods Health Canada’s guidance names, EN 12791 (a European standard) and ASTM E1115 (a North American one), were written for surgical hand antisepsis. The idea is to count the bacteria on volunteers’ fingertips, apply the product, count again immediately, put gloves on the volunteers, wait hours, and count once more. A product with persistence keeps the count down under the glove.

Health Canada’s guidance sets three important conditions:

• Persistence claims are restricted to bacteria. A product can’t claim to keep viruses or fungi away for hours.
• The product must perform “not significantly worse than the reference product” in those tests. It’s a comparison, not a stopwatch.
• For surgical scrubs and pre-operative skin preparations, the guidance expects a persistent effect of at least 6 hours.

The US FDA takes a similar view. In its 2017 final rule on health care antiseptics, it explains why persistence matters for pre-operative skin preparation: cutting through the skin’s barrier over a large area, in a procedure that can last hours, means bacterial regrowth is a real risk. That’s the situation the tests were built for: gloved, unmoving hands in an operating room.

Why the claim has to be authorized in Canada

In Canada, a hand sanitizer is a drug or natural health product, and every claim on its label is part of its authorization.

Most consumer sanitizers are licensed under Health Canada’s monograph for antiseptic skin cleansers for personal domestic use. The monograph spells out what those products can say: that they’re antiseptic or antibacterial cleansers, and that they kill harmful bacteria or germs. It expressly does not support “kills 99.9 percent of germs” claims. Persistence, “long-lasting”, “up to X hours” and “resists wash-off” aren’t in the monograph at all. A product that wants to make them has to apply outside the monograph stream, with its own efficacy data.

Health Canada’s hand sanitizer page adds two rules of thumb. Every authorized product has an eight-digit NPN or DIN on the label, and the department keeps a searchable list. And no hand sanitizer in Canada has been authorized with claims related to COVID-19, whatever the duration promised.

So the practical test for you is simple. If a label says “protects for hours”, the company should be able to show that Health Canada authorized that wording, with data. If it’s a monograph product with a persistence claim added on the front, the claim is off-label.

What “resists wash-off” involves

“Resists wash-off” is a persistence claim wearing a different coat. It implies that the active ingredient bonds to the skin and survives hand washing, so the protection carries on after the sink.

There are two problems. First, Health Canada’s guidance doesn’t describe a wash-off test at all; the persistence methods it recognizes involve gloved hands, not sinks. A company making the claim would need to justify its own method. Second, washing is designed to remove films from the skin. Soap lifts oils and residues; that’s its job. A film that truly survives repeated washing would be unusual, and the evidence for it should be shown, not assumed.

Until you see that evidence, the sensible reading of “resists wash-off” is: this product leaves a residue, and the company hopes some of it stays. Wash your hands as if it didn’t.

What the studies actually show

The published research on persistence comes mostly from surgical settings, and it’s sobering even there.

A 2017 study in Antimicrobial Resistance and Infection Control tested two surgical hand rubs on 25 volunteers using a modified EN 12791 protocol. An alcohol-only formulation reduced bacteria by about 1.96 log immediately (roughly a hundredfold) and still by about 1.67 log after 6 hours under surgical gloves. A chlorhexidine-alcohol combination, the classic “persistent” ingredient, did worse at both time points: 1.42 immediately and 1.24 at 6 hours. The authors concluded chlorhexidine isn’t essential for persistence. So the ingredient marketed for residual effect wasn’t the reason the effect lasted.

A 2018 cross-over trial in the journal Medicine tested 4 percent chlorhexidine and 3 percent chloroxylenol scrubs against a propanol reference under the same European standard. Neither met the standard. Both failed to reduce bacteria on the hands immediately, and after 3 hours under gloves, bacterial counts had increased.

Two lessons follow. Persistence, when it exists, means “less regrowth than there would have been”, not “zero germs”. And it’s measured under gloves, on hands that touch nothing. The moment you touch a doorknob, a phone or a child, you pick up new organisms that the residue on your skin was never tested against.

Reading a “long-lasting” label honestly

A checklist for the store:

• Is there an NPN or DIN? If not, the product isn’t authorized in Canada, and nothing on the label counts.
• Is the duration claim part of the authorized wording? Health Canada’s list shows what each product was licensed for.
• Is it bacteria only? Persistence claims about viruses aren’t permitted under Canadian guidance.
• What’s the active ingredient? Alcohol at 60 percent or more kills fast but doesn’t persist. Residue-formers may persist, but the CDC-reviewed evidence for alcohol-free actives against some germs is weaker, which we cover in our article on alcohol-free sanitizers.
• What would you do differently if the claim were true? If the answer is “sanitize less”, the claim is costing you more than it gives.

Persistent activity is a legitimate scientific idea with a real regulatory definition, useful in operating rooms. On a bottle at the checkout, it’s mostly a reason to keep your hand hygiene the same as it was. You can browse hand care products that have been reviewed for the claims they make. If your hands are sore from sanitizing, that’s a skin barrier problem worth its own attention, and if it isn’t better after two weeks, see your doctor or pharmacist.

Keep the plain version in mind: a sanitizer works when you use it; whatever it leaves behind is a bonus, only for bacteria, only if Health Canada authorized the claim, and never a substitute for the next wash.