Is Foaming Soap Really Just All Fluff and Bubbles?

If you ask Google whether foaming soap is as good as regular liquid soap it's likely you'll be faced with a whole bunch of articles that encourage you to believe that no, it is not. But it doesn't take long to realise that something a bit weird is going on, that the bunch of articles that keep rising to the top of the search rankings seem to be citing the same study.

The study in question was published in the American Journal of Infection Control on 1st July 2017 and it did find the foaming soap to be less effective than liquid soap at removing microbes from the skin but it also concluded that the results weren't statistically robust enough to warrant drawing a hard-and-fast conclusion. So why is this inconclusive study published nearly three years ago still grabbing our attention? We just had to find out...

The study turned out to be a pilot, or initial ‘look-see' trial involving 10 test subjects split into two groups of five. Subjects were asked to wet their hands, dispense 1 pump of soap onto the pam and wash for 6 seconds before drying for 4 seconds with a paper towel. A second swab was taken and bacterial load was counted. While the foaming soap did decrease the micro load (just under 28% reduction), the liquid soap performed better (over 68% reduction) under test conditions. However, as the trial was very small and the micro reduction with the foaming soap was quite low, the results lacked statistical significance.

In spite of the fact that the study found no concrete evidence of a soap-based scandal, the story went viral in the USA! The Health and Wellness section of NBC's ‘Today' website, CBS networks website, WUSA9's online news site and next-gen kick-ass-women-focused website Refinery29 picked up and re-crafted a Reuters article covering the study and ran with it.

All of the news platforms took the same tact with the story, mentioning that this was a pilot study, but leaving it quite late before elaborating on how such a small study could make it hard to produce statistically valid results. The NBC article was particularly strong in pushing its readers to a conclusion as the casual reader had to get past the ‘leading the witness' paragraph heading stating ‘why foam is less effective' before actual experts were given space to reassure the reader that got this far that we really shouldn't read too much into the study due to reasons stated before.

In terms of how the study was conducted, unsurprisingly all of the articles again took the same track, reporting that ‘standard hand washing techniques' were used. While it is true, that the experiment did standardise its hand washing procedure - 6 seconds wash, 3 seconds paper-towel dry - the recommended hand washing standard for antimicrobial efficacy (what the pilot study was testing) is at least 20 seconds followed by (and this is very important) adequate drying.

According to a paper by the Department of Medicine from the University of Aukland back in 1997, medical staff were observed to dry their hands for an average of 17.7 seconds for males and 13.3 seconds for females using an air dryer and 3.5 seconds (male) and 5.2 seconds (females) when using a cloth towel. This typical behavioural data may have informed the 4 second protocol above but typical is nowhere close to optimal and in this case may make results difficult to interpret as the hands are likely to remain damp and prone to microbe transfer after only 4 seconds of dry time.

The same study found that bacterial loads transferred to and from the skin and different surfaces remained over 50% (skin bacteria to surface) unless drying time was over 10 seconds for towel drying (only 3 seconds were needed for air drying). To achieve less than 10% translocation of bacteria drying time for towel drying needed to be 45 seconds, 20 seconds with an air dryer. This information is often under-publicised by soap manufacturers who have more control over the wet stage of washing than the dry but the data shows how a lack of education in this space could severely limit the efficacy of the soap and put users at risk, maybe more so than worrying about whether the soap foams or not. So again, why did this study take off when it seems so inconclusive and basic?

One possible reason that this small and seemingly inconsequential pilot study received so much attention back in July 2017 may be that in USA at the time, the FDA were releasing their new rules on antimicrobial soap. The FDA had announced an investigation into a number of antimicrobial actives back in 2013 and had made a request to hand soap formulators to provide safety evidence to ‘plug the gaps in our knowledge'. By 2017 it was time for a decision to be made and it was, resulting in the banning of a whole range of antimicrobial actives in every-day house hold soap-based products. This shift in law came off the back of evidence that using ingredients such as Triclosan in regular soap may be fuelling anti-microbial resistance, an important issue and potential threat to global health and wellbeing. It is quite likely that in preparation for such a shift in the legal landscape, companies with some skin in the game wanted to distract, shift or otherwise control the conversation in this space, thus allowing just enough chaos and confusion to buy some time for this to all wash over while they re-formulated and/or re-strategised.

Conspiracy theories aside, there are more mainstream reasons why this study may have sparked the imagination of both the industry and the general public. That reason is likely to be the ‘now what?' thinking.

If, as a manufacturer, your main active, the one you were relying on to get your customers clean gets taken off you, how can you make sure your products still work well in future? How do you reassure your clients that you soap is effective even without than antimicrobial active? Surely any report that gives us some pointers, however flimsy, would be lapped up eagerly. But in hanging out for new evidence did we forget the old? After all, by 2017 foaming soaps had been in mainstream circulation for nearly 20 years already.

Back in the late 1990's, UK based Industrial hand cleaning product manufacturer DEB were putting the finishing touches to their new device. By 1999 the first generic foaming soap system for commercial set-ups was launched touting the following benefits:

Foaming Soaps are:

• More economical, dispending a lower dose of soap per application.
• Water saving due to the fact that the foam is easier to rinse off (office bathrooms account for 65% of the businesses water use on average)
• Better for the environment due to lower surfactant burden.
• Less mess and waste from soap dripping or drizzling.
• Convenient.
• Pleasant to use (according to popular opinion)
• Easier to formulate due to no need to stabilise in a gel base.
• Faster to biodegrade due to no need for polymeric thickener.

Foaming soaps were already popular because of their lower per-dose costs and attractive environmental profile so when the dispensers hit this way of hand washing looked set to take over the world!

Ask any scientist and they'll tell you that what's popular isn't necessarily what's good and so far, all we've established is that foaming soaps are popular, cost-effective, environmentally friendly and convenient. The focus now has to return to whether they can be as effective against microbes as liquid soap.

Another reason why the 2017 pilot study took off may be that there is actually precious little data in the public sphere comparing one type of soap to another. In that situation one has to go back to basics and evaluate how soaps work against microbes in order to establish and rank potential for efficacy.

Soap of all persuasions works in the same way and that is by mechanically removing the microbes from the hands. Even if you remove soap, the act of placing the hands under clean, running water is enough to reduce the germ load – this gives us a clue as to why foaming soaps may not always perform well. Once you add soap into the mix you have both the stream that carries the dirt away and the chemistry to rip and hold the dirt and germs off the skin and into the wash water.

In order for both the soap and the water to be effective, they need to be given some help by us and we do this by rubbing our hands with some vigour. The friction and movement of the hands together, between fingers and into the surrounds of the nail bed help us to locate and dislodge the dirt ready for it to be washed away. Again, we are presented with another clue as to why foaming soap may sometimes fall short. Liquid and bar soap requires an investment of friction from us before the foam appears while foaming soap rewards us instantly. Could it be that the only reason that foaming soap could fail us is in how it could make us lazy? If we assume that this much-touted pilot study was onto something and that foaming soaps could fall short, knowing how and why could help us to bridge that gap. It seems more likely that deficit lies more in human behaviour than in the formulation given that while it is true that foaming soaps contain less surfactant as actives per wash-dose, they still contain more than enough to get the hands and body visibly clean. While changes in human behaviour are somewhat difficult for soap makers to control we already know that the people are on our side thanks to that earlier work by DEB and their fancy dispensing machines. People prefer foaming soap, businesses prefer foaming soap and foaming soap is even a winning solution out in locations where general sanitation is deficient.

The Google search that led us to believe that foaming soap may be a problem was built on pre Covid-19 intelligence. Since this pandemic hit, it's hard to find anyone who hasn't internalised the need for longer, more thorough hand washing, drying and sanitising as a way of slowing the spread and flattening the curve. The 2017 pilot study used sub-optimal techniques to measure the efficacy of both types of soap because in the real-world people were generally washing their hands in a sub-optimal way and not just by a little bit. With that in mind we see that this isn't an issue of substance, this is one of application.

Attitudes towards hand hygiene have evolved since then and evolved rapidly. It's more than possible to look beyond the figures in that pilot study and see that foaming soap has potential – indeed, it's been a staple in communal bathrooms around the world for nearly twenty years! Maybe now we are mature enough to read that study and understand that no product works well if we don't use it appropriately.

I'm confident that foaming soap can deliver all the cleaning we need plus some extras in terms of benefits for the environment, our skin, back pocket and bathroom cleanliness just as long as we appreciate the need to apply a little more friction than we have become accustomed to for this product. The only thing we can accuse foaming soap of doing is facilitating our laziness and with that in mind, it may well be time to stop blaming the soap and start scrubbing.

New Directions sells foaming bottles, foaming antimicrobial soap and foaming cleansers for all your face, body and hand formulation needs.

Amanda Foxon-Hill

Reference

1. Foam or liquid soap — which is better?. (2017). Retrieved 1 May 2020
2. Hoskins, J. (2017). Foam soap may not measure up to liquid soap. Retrieved 1 May 2020.
3. PATRICK, D., FINDON, G., & MILLER, T. (1997). Residual moisture determines the level of touch-contact-associated bacterial transfer following hand washing. Epidemiology And Infection, 119(3), 319-325.
4. Dixon, N., Morgan, M., & Equils, o. (2017). Foam soap is not as effective as liquid soap in eliminating hand microbial flora. Retrieved 1 May 2020