Washing hands with soap and water is recognised as the most effective way to clean hands of dirt and infectious microorganisms. In healthcare settings it has been regarded as one of the most important components of infection control since it was shown to reduce maternal mortality tenfold in a Viennese hospital in 1847.
Despite that early knowledge, and much subsequent research showing the benefits, hand hygiene in all settings continues to be a problem today — over 170 years later! The first Global Handwashing Day was initiated by the UN in 2008 to highlight the need for better practice. It has become an annual event to try and raise awareness worldwide of its importance for public health and even international development.
With the COVID-19 pandemic sweeping across the world in 2020 handwashing has been promoted by WHO and national health agencies as one of the main pillars for preventing transmission. For healthcare and food businesses handwashing has always been a high priority, but now all businesses and institutions should be aware of the need to have suitable facilities for handwashing to ensure they minimise the spread of infections. This is important for both respiratory infections and diarrhoea-related illnesses – 30% of which are caused by hand-borne infections, according to the US Centers for Disease Control (CDC).
While the act of washing with soap and water has received most of the attention in cleaning hands, very little has been said about the importance of hand drying as a crucial step in the complete process. Below I explain why hand drying is an important final process for maintaining hand health and preventing transmission of infections, starting with the steps for effective handwashing.
The hand washing process
Hand washing consists of a series of processes that use chemical and physical actions to loosen and remove dirt and microorganisms safely. Each step can reduce the quantity of microorganisms by a factor of up to 10,000, if done correctly. The hand washing process involves the following steps.
1. Wetting hands to loosen dirt
- Washing hands involves:
- applying soap – chemical action dissolves dirt
- water to aid the soap
- rubbing using mechanical energy to help the action of soap all over the hands
- time spent washing
- Rinsing involves:
- water to mechanically remove soap and dirt and dissolve and dilute residues
- time spent rinsing residues away
- Drying has two main actions:
- paper and cloth towels use mechanical action and absorption to remove residues
- air dryers use air movement to mechanically remove moisture and heat to evaporate moisture (ambient heat in jet blades)
Reasons for hand drying
- To reduce the number of infectious microorganisms
Microorganisms play an important role in skin health. Skin carries beneficial, harmless and unwanted microbes, which are classified into two types: the resident and transient flora. The resident flora is permanent and inhabits the outer and surface layers of the skin. These quickly recolonise the skin surface after washing. It can include infectious species such as Staphylococcus aureus, which infects wounds and causes diarrheal disease when transmitted to food.
The transient flora only colonises the superficial layers of the skin and is picked up from contact with contaminated sources such as surfaces and liquids. These include the gut, nose, mouth and other parts of the body, as well as all the objects we touch in our daily lives. They survive on the skin, but do not usually multiply because the environment is too harsh – unless the hands are wet.
The transient microbes are removed by washing and drying, if done properly, protecting both ourselves from transmitting the transient flora to our mouth, nose or eyes, and to others by preventing transmission to other surfaces that people touch. However, even if this reduces the quantity by a factor of 10,000, there may be enough of some pathogens remaining to cause an infection – Norovirus only requires around 10 particles to be infectious and SARS-CoV-2 between 300 and 2000.
Wet hands give a beneficial environment for the transient microorganisms to survive in. They have a far higher quantity of microorganisms on the skin than dry hands and are more effective at transferring them to touched surfaces. Drying hands reduces the translocation of microorganisms to different surfaces, including food, by 94–99.8%.
- To prevent recontamination of the hands
Providing effective and attractive hand drying facilities that encourage people to use them helps prevent people from drying their hands on their own clothes or walking away with wet hands. Touching surfaces with wet hands increases the number of microorganisms picked up.
A study of hand hygiene behaviour in Hong Kong found about 40% of the general public used their own clothing to dry hands some of the time. This could recontaminate hands with dirt their clothes have picked up from the environment or microorganisms in toilet sneeze. It’s certainly bad practice for people handling food, where food could contaminate clothing, and in healthcare settings where clothing could be contaminated from contact with patients.
- Personal comfort
Wet hands feel uncomfortable, so the natural reaction is to want to dry them. Businesses should offer customers and staff a method of hand drying that is most suitable for their situation and that people are more comfortable using. Tissues and cloth towels are quick and effective, while hot air dryers take a longer time to dry and jet blade dryers also dry quickly but are noisy.
In occupations that require frequent hand washing, such as in healthcare, availability of a convenient rapid drying method encourages drying and reduces the risk of unwanted microorganisms colonising the wet skin. Hands that remain damp for long periods can also allow Staphylococcus aureus to become part of the resident skin flora.
- Removing more dirt
Washing properly with soap then rinsing the soap and dirt away, all for at least 20 seconds, should remove the vast majority of dirt from the skin surface. However, if not done properly or the dirt is difficult to dissolve there will be some remaining. The friction from rubbing hands with tissue or cloth removes more dirt after washing — and also remaining microorganisms – and contains them in the fibres.
How to choose the best hand drying solution
Hand drying is an essential part of hand hygiene. There’s a range of hand drying options for businesses and institutions to consider in choosing the best one for their situation – paper towels, cloth roller towels, hot air dryers and jet blade dryers, each with advantages and disadvantages. When considering which drying method to select, factors to consider include:
- costs for hardware, installation and maintenance
- hand drying efficiency – speed of drying
- comfort in use, including noise
- preferences of users
- sustainability, including energy and raw materials used
- dispersal of microorganisms during use
Within each hand drying method there can be wide variation depending on, for example, sources of supply, energy sources used and model of dryer. Making the optimal choice can be complicated and is covered in more detail in our white paper.