Wet wipes antibacterial efficacy: what "log reduction" means

3 octobre 2026

Gloved hand using a disinfectant wipe on a hard clinical surface

A log reduction is the base-ten logarithm of how far a microbe count fell. One log means a 90% reduction, three logs mean 99.9%, and five logs mean 99.999%. Health Canada's efficacy guidance for hard-surface disinfectants sets those numbers against specific claims and contact times, and for a wipe the contact time is tied to how long the surface stays wet rather than to how hard the surface is rubbed.

The word "log" is doing ordinary arithmetic rather than anything exotic. It is the shorthand for "divide the starting count by ten, this many times", which is why a higher log number is dramatically harder to reach than a lower one.

What is a log reduction?

A log reduction is the common logarithm of the ratio between the number of organisms before a process and the number after it, so each additional log is another factor of ten. The table converts the figures a clinic is most likely to see on a label or in a test report.

Log reduction	Percentage reduction	Survivors, per million organisms
1 log	90%	100,000
2 log	99%	10,000
3 log	99.9%	1,000
4 log	99.99%	100
5 log	99.999%	10
6 log	99.9999%	1

Read the table the other way: a 3 log claim still leaves a thousand survivors per million organisms, and a 6 log claim leaves one.

What log reduction does a disinfectant have to reach?

The threshold depends on the claim the product makes and on the test method. Health Canada's guidance for hard-surface disinfectant drugs states, for the bactericidal claim, that "a 99.9% mean reduction (3 log10 minimum) for each bacterium must be demonstrated within a 5 minute contact time, unless otherwise prescribed in the test method." The same document pairs other claims with higher figures.

Claim	Performance criterion in the guidance
Bactericidal, hard surface	A 99.9% mean reduction, or 3 log10 minimum, for each bacterium, within a 5-minute contact time unless the test method says otherwise
Food-contact surface, non-halide	A 5 log10 reduction for each bacterium within a 30-second contact time
Mycobactericidal	A minimum geometric mean inoculum of 1 x 10 to the 4 colony forming units per carrier for a valid test
Sporicidal	A mean 6 log10 reduction based on recoverable spores within the proposed contact time

The variants matter because a product's label carries the claim it was tested for, not a general strength. A wipe labelled as bactericidal is not the same product as a wipe tested to a sporicidal criterion, even when both look identical on the shelf.

How does a wipe's wetness affect the result?

For a single-use wipe, the wetness is not incidental; the guidance builds the contact time from it. Health Canada's document states that, for testing single-use towelettes on the basis of the expressed liquid, "a determination of the amount of time the carrier remains wet should be made", and that this wetness determination is used to generate the contact time used in the efficacy test. In other words, the contact time printed for a wipe is anchored to how long the surface stays wet under test, so a wipe that dries out early on a warm or absorbent surface is being used outside that assumption.

Independent testing reaches the same conclusion. A 2021 study applying the EN 16615 four-field test to commercial and self-made wipes states the pass criterion for that method: the decimal log reduction in the first field must be "at least 5 logs (bacteria) and 4 logs (yeast)", with the average number of cells in the remaining fields not exceeding 50 colony forming units. Its authors also attribute the weaker result of some sodium hypochlorite wipes to how the active and the wetness behaved on the surface.

What a log claim does and does not tell you

A log reduction tells you how far a count fell in a defined test, against a defined organism, chemistry and contact time. It does not tell you that a surface is sterile, that a wipe will perform the same way on a soiled or porous surface, or that a wipe used once will keep working after it has dried. For clinic use the practical reading is: match the claim to the job, and give the surface the wet contact time the label asks for. Wipes built for hospital-grade disinfection are catalogued through the disinfectant wipe range, and facilities setting a single specification across sites can use the wholesale and institutional account page.

For the records side, the same document set shows what a clinic used and when, and the printable sterilization log sheet and label generators build those fields without an account.

Have a question about your own facility? Send it in and you will get a written answer specific to your setup, with the regulation or standard it is based on cited. Ask your compliance question.

Frequently Asked Questions

Is a 3 log reduction the same as 99.9%?

Yes. A 3 log reduction is a 99.9% reduction, because each log is a factor of ten: 1 log is 90%, 2 log is 99%, and 3 log is 99.9%.

What log reduction is needed to call a wipe a disinfectant in Canada?

For the bactericidal claim, Health Canada's guidance uses a 99.9% mean reduction, or 3 log10 minimum, for each bacterium within a 5-minute contact time unless the test method states otherwise. Higher claims, such as a sporicidal claim, are tied to higher figures.

Does a higher log number mean the product is stronger on every surface?

No. The log reduction applies to the organism, chemistry and contact time the product was tested against. A high figure on a clean, hard surface does not carry over to a soiled or porous one, or to a wipe that has dried out before the contact time elapsed.

Why does a wipe's contact time depend on staying wet?

Because the guidance for single-use towelettes builds the contact time from how long the carrier remains wet under test. If the surface dries before that time, the wipe is being used outside the condition its contact time was generated from.

Does a log reduction claim mean the surface is sterile?

No. A log reduction is a measured fall in a count, not a statement that no organisms remain. Sterility is a separate claim, and for surfaces the correct reading is the log reduction against the stated organism and contact time.

Canister of hospital-grade disinfectant wipes for surface cleaning

CliniEco Medical holds Medical Device Establishment Licence MDEL #35334. This article summarises published federal guidance and peer-reviewed testing for information only; it does not replace the product's own label and instructions, provincial infection prevention and control requirements, or the guidance of the relevant regulator for a specific product.