Analysis of hand environment factors contributing to the hand surface infection barrier imparted by lactic acid

Abstract

Background Organic acids on the surface of human hands contribute to the barrier against transient pathogens. This is the first study to explore the synergistic contribution of lactic acid and other hand environment‐related features on the antibacterial properties of the hand surface. Materials and Methods We estimated the contribution of fingerprint depth, skin pH, stratum corneum water content, skin temperature, and sweat rate of the hands to the infection barrier using an observational survey of 105 subjects. The relationship between each factor and the antibacterial activity of the hands was analyzed using Pearson's correlation coefficient. We performed molecular dynamics simulations to study the interaction between lactic acid and bacterial membranes. Results The amount of lactic acid on the hands and skin temperature contributed positively to the antimicrobial activity (r = 0.437 and P = 3.18 × 10−6, r = 0.500 and P = 5.66 × 10−8, respectively), while the skin pH contributed negatively (r = −0.471, P = 3.99 × 10−7). The predicted value of the combined antimicrobial effect of these parameters was [antimicrobial activity] = 0.21 × [lactic acid] − 0.25 × [skin pH] + 0.26 × [skin temperature] + 0.98. The coefficient of determination (R2) was 0.50. Conclusion The increase in the amount of non‐ionic lactic acid due to lower pH and improvement in the fluidity of the cell membrane due to higher temperatures enable the efficient transport of lactic acid into cells and subsequent antimicrobial activity. The proposed mechanism could help to develop an effective hand infection barrier technology.

Association Between Skin Acid Mantle, Natural Moisturizing Factors, and Antibacterial Activity Against S. aureus in the Stratum Corneum

“… 20 Antibacterial activity of skin is normally studied by inoculating target microorganisms directly onto the skin. 11 , 21 Here, an ex vivo method was developed to study S. aureus ATCC 6538 viability on human SC. S. aureus was directly inoculated on human SC collected by adhesive discs.…”

“…Namely, Hayashi et al demonstrated that skin pH negatively correlated with the antibacterial activity of the hands against E. coli . 11 Colonization of the skin with the gram-positive bacteria Staphylococcus aureus ( S. aureus ) is a major pathogenic factor in AD. 12 Notably, the skin pH is higher in patients with AD than in healthy controls, even on uninvolved sites without lesions.…”

The pH of the lip surface

“…1 New research indicates that lactic acid is a contributor factor in maintaining the skin surface pH and along with temperature may be responsible for the antibacterial properties of the hand surface. 2 The lips (vermilion) differ from skin on the rest of the body in that they are covered by nonkeratinized, stratified, squamous epithelium.…”