November 2021

A Word About Soap, Water and Hand Sanitizers

The roles of soap and water versus hand sanitizers for SARS-COV-2 decontamination.

Hand sanitizers are an important hand hygiene intervention for skin contaminated with an enveloped virus such as SARS-CoV-2. Sanitizers are packaged in units that can be carried easily and therefore are able to be used in high-risk situations (eg, following contact with high-touch environmental surfaces in public places) where the opportunity to wash hands with soap and water is not always possible. In addition, alcohol-based hand sanitizers appear to have less potential for causing skin irritation than do soaps. One needs to be cautious, however, particularly with repeated use of hand washing with soap immediately before or after using an alcohol-based product under healthcare settings, as this practice could lead to dermatitis. Therefore, we recommend that hand sanitizers not be used when soap and water hand wash facilities are available.

Alcohol-based hand sanitizers were found by Grayson et al to be more effective than hand washing in reducing human influenza A virus on human hands, though both interventions were found to be effective. For disinfection of hands contaminated with SARS-CoV-2, a variety of types of hand sanitizers should be effective. These include alcohol-based sanitizers (≥60% ethanol or ≥70% isopropanol content is recommended per the United States Centers for Disease Control & Prevention (CDC). In general, lower concentrations of alcohols (~60%) are effective for inactivation of enveloped viruses, while higher concentrations (70% to 80%) are required for inactivation of non-enveloped viruses, such as hepatitis A and poliovirus.

Table 1 reprinted from Mukherjee S, Vincent CK, Jayasekera HW, Yekhe AS. Antiviral efficacy of personal care formulations against Severe Acute Respiratory Syndrome Coronavirus 2. Infect Dis Health. 2021;26(1):63-66. doi:10.1016/j.idh.2020.09.003. Use is per the COVID-19 Resource Centre from Elsevier.

Golin, Choi & Ghahary have reviewed the efficacy of a variety of hand sanitizers against coronaviruses. These authors also reviewed the relatively limited empirical data obtained from studies directly comparing the efficacy of hand sanitizers vs. hand soaps for inactivating enveloped and non-enveloped viruses. Steinmann et al evaluated virucidal efficacy against enveloped viruses (vaccinia virus and bovine viral diarrhea virus) and non-enveloped viruses (poliovirus, adenovirus, feline calicivirus, and murine norovirus), comparing alcohol-based hand sanitizers with antimicrobial soaps in suspension testing and the fingerpad test with 30s contact time. In the suspension testing method, the sanitizers were effective against all viruses, whereas the soaps were effective against the enveloped viruses only. In the fingerpad test, a povidone-iodine-containing soap was superior to the sanitizers, while the other soaps (containing chlorhexidine or triclosan) displayed less activity. In the Tuladhar et al study, the virucidal efficacy of a propanol-based disinfectant against the non-enveloped murine norovirus was compared with that of soap and water. Soap and water washing was found to be superior to the propanol-based sanitizer, causing complete (≥3.0 ± 0.4 log10) inactivation within 30s, while inactivation by the alcohol-based sanitizer was incomplete and variable (2.8 ± 1.5 log10) and required greater contact time (3 min).

The efficacies, for inactivating SARS-CoV-2, of three bar soaps and three alcohol-based hand sanitizers were compared in Mukherjee et al (see Table 1). Each resulted in complete (≥3 to ≥4 log10 inactivation), though the test conditions were not the same. For instance, the bar soaps were tested as an 8% solution at 40 degrees C for 20s, while the hand sanitizers were tested undiluted (as supplied), at 20 degrees C, for 10 or 15s. Wolfe et al compared the virucidal efficacy of soap and water vs. an ethanol-based hand sanitizer against the enveloped bacteriophage Phi6 (used as a surrogate for the Ebola virus) spiked onto human hands in the presence or absence of a soil load. In the absence of a soil load, the reductions in phage titer obtained following soap and water washing vs. use of the ethanol-based hand sanitizer were approximately equivalent (~2.5 log10), while in the presence of a soil load, the efficacy of soap and water was superior (3.7 log10 vs. ~2.5 log10 for the hand sanitizer).

Figure 1 Routes of transmission of respiratory and enteric viruses, such as influenza, MERS-CoV, and SARS-CoV-2.

The comparison data mentioned above suggest that both hand sanitizers and soap and water display virucidal efficacy for enveloped viruses over short contact times (30s). Hand washing with soap and water is recommended by the CDC and the World Health Organization, when possible, since this hygiene practice achieves pathogen reduction both through removal and inactivation mechanisms, as alluded to above. This is in agreement with findings reported by Foddai, Grant & Dean. In contrast, an alcohol hand rub (ABHR) or other type of hand sanitizer would be expected to inactivate but not necessarily remove infectious virus from the hands. As is the case for hand washing, the effectiveness of hand sanitizers is dependent on the contact time the active ingredient is in contact with the skin, and on the thoroughness of application of the sanitizer to all parts of the hand. According to the CDC:

  • Alcohol-based hand sanitizers can quickly reduce the number of microbes on hands in some situations, but sanitizers do not eliminate all types of germs.
  • Hand sanitizers may not be as effective when hands are visibly dirty or greasy.
  • If soap and water are not available, use an alcohol-based hand sanitizer that contains at least 60% alcohol.
  • When using hand sanitizer, apply the product to the palm of one hand (read the label to
  • learn the correct amount) and rub the product all over the surfaces of your hands until your hands are dry.

This article is excerpted from Ijaz MK, Nims RW, de Szalay S, Rubino JR. Soap, water, and severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2): an ancient handwashing strategy for preventing dissemination of a novel virus. PeerJ. 2021;9:e12041. Editing, including removal of the references, for brevity has occurred. Use is per the Creative Commons Attribution License. The full article is available at doi:10.7717/peerj.12041.

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