Using hand sanitizer won't necessarily kill 99.99 per cent of germs on your hands despite the claims made by many such products, a CBC investigation has found.

CBC News tested three popular sanitizers — top-selling Purell, President's Choice and Soapopular — on a class of Grade 8 students at Ryerson Middle School in Hamilton, Ont., last month.

President's Choice and Purell both contain alcohol, while Soapopular contains no alcohol but rather the anti-bacterial agent benzalkonium chloride.

Students were divided into three groups of six and a different hand sanitizer was assigned to each one.

The CBC enlisted the help of microbiologist Jason Tetro of the Ottawa-based Centre for Research on Environmental Microbiology.

Dirty hands undermine sanitizers' effectiveness    

People should really be washing their hands between eight and 12 times a day for hand sanitizers to work effectively, microbiologist Jason Tetro says.

"We're not asking you to wash your hands the way we do in the lab, where it could be upwards of 20 times a day," Tetro said. "You have a minimum of about eight to 12 situations where you should have been washing your hands, and if you're not, you're not following good hygienic practices."

Tetro, of the Ottawa-based Centre for Research on Environmental Microbiology, said the bottom line is that dirty hands limit the effect of hand sanitizers.

"Essentially, it's the soiling of hands that can prevent a hand sanitizer from working properly," Tetro said.

"Alcohol [in sanitizers] acts through the denaturation of proteins and DNA. If there is a significant amount of dirt and oil on the hands, the alcohol cannot act as efficiently and may not kill bacteria and viruses in the same way.

"This supports the recommendation that cleaner hands lead to better alcohol hand sanitizer activity," he said.

Some of CBC's test results were particularly surprising: A few kids who were tested actually had an increase in germ count after using hand sanitizer.

Tetro explained that phenomenon, saying that hands can be so dirty that bacteria is protected from sanitizer.

"When dirt and oil accumulate, this can lead to 'clumping' of bacteria, which can then be broken down and spread using the hand sanitizer. This could lead to the observed higher level," he said.

"The thing is [hand sanitizers] will not completely remove the risk of infection to bacteria and viruses. They work very well with regular hand washing and also in an environment where you don't have soap and water, they will help you to reduce that risk. But the risk is never going to be eliminated by these products," he said.

The students weren't asked to wash their hands before the test. They began the test with their fingers contaminated by whatever they had touched on a lunch break.

Tetro took swabs of their hands to get a baseline measure of the bugs and germs lurking around fingernails and in creases.

Students then liberally rubbed their hands with sanitizer. A second swab was taken and the results were sent to Tetro's lab. He helped explain them once they came back.

And they needed a little explaining.

Test results

President's Choice killed an average of 54.6 per cent of microbes on the kids' hands. Purell killed about 60.4 per cent. And Soapopular killed 46 per cent.

So why did CBC's results differ so much from the claims on hand-sanitizer bottles and websites?

According to Tetro, the companies are not deliberately misleading consumers. They've had to test their products in accredited labs before Health Canada would allow them to make the 99.99 per cent claim.

Tetro knows this because he's carried out hundreds of similar tests.

"The claim is based on these very controlled laboratory tests and we do those tests here at the lab," he said.

When hand sanitizers undergo testing, the hands they're tested on are first sanitized in the lab, then sprinkled with microbes in a controlled situation.

"We wash the hands. We make sure they are clean and devoid of any germs, then we artificially put the germs on their finger pads. Then we test to find out whether the product kills or eliminates it," said Tetro.

Grease and grime protect germs

Hand sanitizers don't work as well on really dirty hands because grime and grease actually protect germs from being destroyed.

"In a real life situation, we don't know how clean those hands are and so you're not going to see anywhere near the type of results [identified on the bottle]," Tetro said.

All three firms were critical of CBC's test results.

"We feel the methodology used by CBC is unscientific and therefore the result is not representative of President's Choice hand sanitizer's true potential," wrote David Primorac, senior director of public relations for Loblaw Companies Ltd., which sells President's Choice products.

"We clearly believe the 54 per cent results achieved by the CBC are inaccurate and misleading," wrote Primorac, who also questioned whether the students were tested in exactly the same method under controlled conditions.

"I ask these questions because we get these inquiries now and again and it is extremely important that this is an apples-to-apples comparison. The slightest deviation can skew results," Primorac wrote.

Test conditions not 'real world': Loblaw

He said Loblaw has tested its sanitizer in "real world" conditions in a Health Canada accredited lab.

"We brought in volunteers from real life situations and measured the microbial load on their hands before use and after use. Seventy-nine per cent of the subjects achieved 100 per cent kill rate with 21 per cent achieving 99 per cent or over kill rate," Primorac wrote.

Purell said it was "unable to comment on the accuracy of any third-party data we haven't reviewed" and that it was "confident in the science that supports our claims and the efficacy of Purell hand sanitizer."

Soapopular said in a statement that CBC's results were "less than half of any result reported during literally hundreds of previous tests conducted for health and safety agencies in all G8 countries and ministries of health in over 65 countries."

The companies acknowledged that sanitizers are an alternative when soap and water aren't available, but they are not meant to substitute for hand washing.

So it all comes back to the advice that doctors and mothers give all the time: Wash your hands with soap and water.