Innate Antimicrobial Function of the Hands Acts as a Barrier Against Infectious Diseases

Contact infection is one of the key transmission routes of infectious diseases. It means the route of infection where healthy individuals become infected by direct physical contact with infected individuals, or by indirect contact through contaminated door knobs, toilets, smartphones, etc. As the human hands have both a sensory function to identify objects by touching and a movement function to hold objects, they play a significant role in contact infection.

As humans have co-existed with bacteria and viruses throughout their long history, our bodies are thought to have evolved various immune functions to protect against infectious diseases. For example, antibodies are an immune function that exists inside the human body. Kao focused on the surface of the human body which interfaces with the external environment to see what kinds of protective mechanism are present against many pathogens. As the hands are key parts of the human body that contact with the external environment as described above, they seemed likely to have some ability to control the pathogens.

To test this hypothesis, Kao's researchers conducted the study, first by examining the characteristics of the hands of individuals with high and low resistance to infectious diseases to identify differences between the two groups.

As a preliminary experiment, the researchers first selected several volunteers who thought they were either highly resistant or susceptible to infectious diseases. The experiment revealed that the existence of the bacteria diminished significantly after three minutes on the hands of individuals who thought they were highly resistant to infectious diseases (Figure 1).

A pool of 109 healthy male and female volunteers aged between 20 and 49 were selected, of which 55 were known to have low resistance to infectious diseases, while 54 were known to have high resistance^*4 . Then, samples on the surface of their hands were collected to evaluate their antibacterial activity. The study revealed that the samples from the volunteers with high resistance to infectious diseases had significantly high antibacterial activity against both E. coli and S. aureus (Figure 4). This finding strongly suggests that those volunteers' hand surface infection barrier had contributed to their resistance to infectious diseases.

A pool of 54 male and female volunteers in their 20s to 40s were selected, and then samples of what were on the surface of their hands were collected for evaluation, in order to identify the compounds that were highly correlated to the antibacterial and antiviral activity against S. aureus and the influenza A virus (H3N2). The results showed that the lactic acid secreted from the hands was playing the key role in this activity (Figure 5), among the several compounds that had exhibited a high correlation to both pathogenic microorganisms.

In another experiment where a lactic acid solution was applied to the volunteers' hands with varying amounts of lactic acid within the range that exists on human hands, it was confirmed that the antibacterial activity increased as the amount of lactic acid increased (Figure 6).

Conventional hand hygiene methods such as hand washing and alcohol-based hand sanitizers have only transient effects of removing and inactivating bacteria and viruses. In contrast, the characteristic of the inherent hand surface infection barrier function is that it is permanent. The discovery of this hand surface barrier could lead to new suggestions on hygiene behavior to enhance the inherent barrier function of the hands. In the future, Kao will continue its in-depth research on the hand surface infection barrier function and propose new hygiene behaviors in order to contribute to the realization of infection prevention behavior that will protect people around the world from various infectious diseases as well as from the distress they cause.

Kao creates high-value-added products that enrich the lives of consumers around the world. Through its portfolio of over 20 leading brands such as Attack, Bioré, Goldwell, Jergens, John Frieda, Kanebo, Laurier, Merries and Molton Brown, Kao is part of the everyday lives of people in Asia, Oceania, North America and Europe. Combined with its chemical division, which contributes to a wide range of industries, Kao generates about 1,500 billion yen in annual sales. Kao employs about 33,000 people worldwide and has 130 years of history in innovation. Please visit the Kao Group website for updated information.