In light of the COVID-19 pandemic, I thought it would be apropos to discuss the different types of hand sanitizers available and how to evaluate their efficacy in killing germs.
All hand sanitizers are not the same. Specific ingredients do make a difference in antimicrobial action. Choose a hand sanitizer based on what specific bacteria, fungi and viruses you wish to inactivate. There isn’t a hand gel that kills everything. Furthermore, even if that did exist, it would be associated with negative health consequences.
There are hand sanitizers advertised as “alcohol-free,” presumably the advantage being that there is less drying out of the skin. These products contain benzalkonium chloride, a chemical that is effective against many bacteria, some fungi and protozoa. It is not effective against Mycobacterium tuberculosis, Pseudomonas bacteria, bacterial spores and viruses. Benzalkonium chloride is readily inactivated by the presence of blood and other organic matter – dirt, grease, etc. – that may be present on skin. Any residual soap on the skin will neutralize its antiseptic effect. It also tends to become easily contaminated with gram-negative bacteria.
The use of these hand sanitizers is not recommended for disinfecting yourself against coronaviruses.
Alcohol is effective against gram-positive and gram-negative bacteria, many fungi and all lipophilic viruses (herpes, vaccinia, HIV, influenza and coronavirus). It is not effective against nonlipid viruses. It is virucidal for hydrophilic viruses such as astrovirus, rhinovirus, adenovirus, echovirus, enterovirus and rotavirus. Alcohol does not kill polio virus or hepatitis A virus. It also does not provide continuous antimicrobial activity once it has dried. Therefore, it cannot be recommended as a stand-alone prevention. The utility of alcohol lies in its combination with more persistent antiseptic agents.
There are two types of alcohol-containing hand gels: ethyl alcohol and isopropyl alcohol; 70% alcohol is effective for killing common pathogenic bacteria but is ineffective against bacterial spores. Maximum effect is obtained by keeping hands moist with alcohol for two minutes. A casual rub for several seconds does not provide sufficient microbial clearing.
Isopropyl alcohol has an advantage over ethanol because it is more germicidal over a wider range of concentrations and is less volatile. A minimum concentration of 62% isopropyl alcohol is needed for antimicrobial effect. Its efficacy decreases with lower concentrations.
Methyl alcohol (methanol) has the weakest antimicrobial action of the all alcohols and is not recommended as a disinfectant.
Povidone-iodine is an antiseptic that is effective against a wide range of germs, including gram-positive and gram-negative bacteria, some bacterial spores, yeast, protozoa, and viruses such as HIV and hepatitis B virus. Antimicrobial effectiveness is determined by the concentration of free iodine in the solution. A minimum of two-minute contact time on the skin is needed for it to be effective. If not removed from the skin, povidone-iodine has sustained activity for one to two hours. The downside of using this as an antiseptic is that skin becomes orange-brown and there is a risk of allergic reactions, including anaphylaxis and skin irritation.
Hypochlorous acid is a naturally occurring molecule produced by the body’s own white blood cells. It has good disinfection ability. It has bactericidal, fungicidal and sporicidal activity. It damages the structural proteins on microorganisms. Hypochlorous acid, available in gel and spray form, can be used to disinfect surfaces and objects. Studies demonstrate virucidal activity against avian influenza A virus, rhinovirus, adenovirus and norovirus. Hypochlorous acid has not been specifically tested on COVID-19. Hypochlorous acid formulations are available over the counter and by prescription. Do not attempt to make one yourself.
Hydrogen peroxide is active against bacteria, yeast, fungi, viruses and spores. It produces hydroxyl free radicals that destroy cell membranes and proteins that are essential for microorganisms’ existence. Hydrogen peroxide decomposes into water and oxygen. Over-the-counter hydrogen peroxide is 3% concentration. Do not dilute it. The lower the concentration, the longer the contact time must be for it to work.
Baking soda is useful for removing stains on surfaces but is completely ineffective for use as an antimicrobial agent.
Although hand sanitizers are helpful in decreasing one’s risk of becoming infected with COVID-19, it is not a replacement for soap and water. So, remember to wash your hands well with soap and water after you return home from running errands.
Dr. Patricia Wong is a dermatologist in private practice in Palo Alto. For more information, call 473-3173 or visit patriciawongmd.com.