Hand hygiene is of utmost importance as it may be contaminated easily from direct contact with airborne microorganism droplets from coughs and sneezes. Particularly in situations like pandemic outbreaks, it is crucial to interrupt the transmission chain of the virus by the practice of proper hand sanitization. It can be achieved with contact isolation and strict infection control tool like maintaining good hand hygiene in hospital settings and in public. The success of hand sanitization solely depends on the use of effective hand disinfecting agents formulated in various types and forms such as antimicrobial soaps, and water-based or alcohol-based hand sanitizer, with the latter being widely used in hospitals settings. To date, most of the effective hand sanitizer products are alcohol-based formulations containing 62%–95% of alcohol as it can denature the proteins of microbes and the ability to inactivate viruses.
The World Health Organization (WHO) defines an alcohol-based hand rub as: “An alcohol-containing preparation (liquid, gel or foam) designed for application to the hands to inactivate microorganisms and/or temporarily suppress their growth. Such preparations may contain one or more types of alcohol, other active ingredients with excipients, and humectants.”
Alcohol-based hand antiseptics mostly contain isopropanol, ethanol, n-propanol, or a mixture of these as their active ingredients. The antimicrobial activity of alcohols is attributed to their ability to denature and coagulate proteins. This causes microbes to lose their protective coatings and become non-functional. The Center for Disease Control and Prevention recommends formulations containing 80% (percent volume/volume) ethanol or 75% isopropyl alcohol; however, generally speaking, sanitizers containing 60 to 95% alcohol are acceptable. The recommended percentages of ethanol and isopropyl alcohol are kept as 80% and 75% because these values lie in the middle of the acceptable range. Notably, higher than recommended concentrations are also paradoxically less potent because proteins are not denatured easily without the presence of water. Alcohol concentrations in antiseptic hand rubs are often expressed as percent by volume and rarely as percent by weight. A study conducted on 85% (weight/weight) ethanol showed that a 15 seconds contact time was enough to reduce gram-positive and negative bacteria by greater than 5 log10 steps.
Research suggests that alcohols are swiftly germicidal when applied to the skin but have no noticeable persistent residual activity. However, it has been documented that the regrowth of bacteria does occur slowly after its use. This may be because of the sublethal effect alcohol may have had on the residual bacteria. Adding chlorhexidine, octenidine, or triclosan to alcohol-based hand rubs may result in somewhat persistent protection as well. 4% chlorhexidine has shown persistent bactericidal activity against methicillin-resistant Staphylococcus aureus for up to 4 hours from application.
Ethanol, the most common alcohol ingredient, appears to be the most effective alcohol against viruses, whereas propanol is considered a better bactericidal alcohol. The combination of alcohols may also have a synergistic effect. The alcohol concentration in hand sanitizers also changes its efficacy, with one study demonstrating that a hand rub with 85% ethanol content was significantly better at reducing bacterial populations than preparations of 60% to 62% ethanol. ABHS also often contain humectants, like glycerin, which helps prevent skin dryness, and emollients or moisturizers, like aloe vera, which help replace some of the water stripped off during use. None of the above-mentioned alcohols have shown a potential for acquired bacterial resistance and are therefore considered highly effective for repeated use in medical settings.