Importance of Hand Hygiene
It is no exaggeration to say that hand hygiene is the most important key to preventing infectious diseases. Infectious diseases transmitted through the respiratory tract, such as COVID-19, are actually often transmitted by touching droplets discharged from patients with their hands. People unconsciously touch their noses and eyes more than 15 times a day on average (J Occup Envir Hyg 2008).
The first important thing for hand hygiene is to wash your hands well. In fact, it is sometimes inconvenient, but there are many daily necessities that cannot be washed with water, such as cell phones that we touch every day. That is why hygiene products such as hand sanitizers and alcohol swabs are commonly used these days.
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| The first step in hand hygiene is washing your hands. |
Can alcohol disinfect COVID-19?
Disinfection refers to the use of relatively weak sterilizing power to suppress or destroy the growth of pathogenic microorganisms and eliminate the risk of infection. Alcohol is a disinfectant widely used to disinfect items that come into contact with human skin, mucous membranes, or healthy skin due to its strong antibacterial power and quick evaporation properties.
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| Ethanol for Disinfection |
Among alcohols, methyl alcohol has a weak sterilizing effect and is not used as a disinfectant. Alcohols used as disinfectants are generally isopropanol (IPA) and ethanol (EtOH). Isopropanol is obtained by the hydration reaction of propene present in the decomposition gas in petroleum oil, and ethanol is obtained by hydrolyzing ethene in coal gas or petroleum oil. Recently, due to the increase in the price of 70% IPA and the problem of concentration management due to human toxicity, ethanol is being used more.
So, can these alcohol preparations disinfect the COVID-19 virus? There are enveloped viruses and non-enveloped viruses. The envelope is composed of lipids of the host cell membrane and virus-specific proteins. Enveloped viruses are composed of 20-35% lipids by weight, of which 50-60% are phospholipids, making them sensitive to lipid solvents and easily inactivated when exposed.
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| Viruses come in enveloped types, like COVID-19 (left), and non-enveloped types, like adenovirus (right). |
COVID-19 is an enveloped virus, and it was named Corona because of the spike protein attached to the outer coat. Alcohol is a lipophilic solvent that dissolves phospholipids and removes the spike protein, which inactivates the COVID-19 virus. This means that alcohol is effective in disinfecting COVID-19.
While enveloped viruses use a lipid envelope for infection, non-enveloped viruses such as adenoviruses use a protein coat for infection, so denaturation of the capsid protein or proteins essential for proliferation is necessary to inactivate them.
Among alcohol preparations, ethanol also has the function of denaturing proteins, so it is effective against some non-enveloped viruses, but isopropanol has been reported to be ineffective (J Hosp Infect. 2018).
Although isopropanol preparations are also effective against the COVID-19 virus, it seems better to use ethanol preparations in many ways, both in terms of safety and for wide-ranging use.
However, if it is used for disinfecting the COVID-19 virus and using alcohol swabs on electronic devices such as cell phones, isopropanol preparations are more suitable for preventing device failure because they evaporate faster.
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| Alcohol preparations include products using isopropanol (left) and products using ethanol (right). |
Alcohol-based disinfectants are used in many ways, but they can damage surfaces and have limited effectiveness, so they are not usually used to disinfect the environment (Centers for Disease Control and Prevention; CDC, 2019). For environmental disinfection, sodium hypochlorite, the main ingredient in bleach, is recommended (VIEW 2020).
Alcohol products have a disinfecting effect due to their lipid-dissolving properties, but they remove oil (phospholipids) from the skin, causing dry skin and contact dermatitis. When I was in the lab, I used to use a lot of alcohol, so my fingertips cracked and bled a lot. These days, there are many products with skin softeners such as glycerol, but it is also a tip to lightly apply a moisturizer such as hand cream after alcohol disinfection.
Why is the ethanol content 83%?
Ethanol shows excellent sterilizing power against all viruses, bacteria, and fungi within 1 minute. It is easy to think that the higher the alcohol content, the better the sterilizing effect, but this is not necessarily the case.
Alcohol sterilizes by denaturing proteins, and since proteins denature faster when there is water, 100% pure alcohol with the moisture removed has a lower sterilizing power than a solution that is a mixture of water and alcohol. The moisture content also has the effect of increasing the sterilizing power by slowing down the evaporation rate and increasing the surface contact time.
So, it is generally recommended to dilute alcohol in water to 60-80% (WHO Hand Hygiene Guidelines, 2007), and 70% (w/v) alcohol is usually proven to be the most effective and safe concentration (US Centers for Disease Control and Prevention; CDC, 2011). At concentrations above 80%, the effectiveness of the disinfectant actually decreases (Archives of Surgery, 1939). That is why 70% ethanol is generally used in hospitals, laboratories, and daily life products (Martindale, 32nd Ed.).
I also used 70% ethanol in the laboratory. However, when I searched for an alcohol swab product, it said that the ethanol content was 83%. Why isn't it 70%? Moreover, it is neither 80% nor 85%, but 83% is too ambiguous, right?
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| 83% ethanol for disinfection |
The standard for ethanol listed in the Korean Pharmacopoeia (KP) is 95.1~96.9 vol%. This means that it contains 95.1~96.9% of pure ethanol. Disinfectant ethanol refers to an ethanol solution made by adding 170 ml of water to 830 ml of ethanol to make 1000 ml. In other words, both ethanol and disinfectant ethanol are indicated in volume units (v/v) according to the KP.
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| Ethanol for disinfection, 83ml of ethanol per 100ml |
According to the WHO Hand Hygiene Guidelines (2007), if it can be affected by temperature, etc., it can be expressed as a percentage by volume (v/v). Alcohol is a substance affected by temperature. For example, 70% alcohol by weight (w) becomes 76.8% by volume (v) when made at 15℃, and 80.5% when made at 25℃. KP sets it at 83% by volume (v/v) at 15℃.
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| 100ml 중 에탄올 83ml인 소독용 에탄올 |
The original concentration unit of 70% ethanol, which has a sterilizing effect, means mass percentage w/w, so let's calculate the weight of pure ethanol in 83% (v/v) ethanol for disinfection.
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| Ethanol content of ethanol preparations for disinfection (alcohol swabs) |
Assuming that 100ml of ethanol is produced, the amount of pure ethanol among the 83ml of ethanol (KP) required is 83ml x 95.1% = 78.933ml if 95.1% ethanol according to KP is used. Ethanol has a specific gravity of 0.789g/ml, so converting this to weight, it is 78.933ml x 0.789 = 62.278137g. Of the 83ml of raw ethanol, excluding 78.933ml of pure ethanol, the remaining volume of 4.067ml and 17ml of distilled water for dilution are the same, 4.067g and 17g, since the specific gravity of water is 1.0. If you calculate it, (62.278137g/4.067g+17g+62.278137g) x 100 = approximately 74.7%. If you use 96.9% ethanol according to KP, it will be approximately 76.4%.
When converting the volume to weight, the ethanol content of ethanol for disinfection is approximately 75% w/w. Usually, the content of finished products of non-medical products is set to 90 to 110% of the labeled amount for quality assurance, but since ethanol is highly volatile and continues to evaporate even in an aqueous solution, it makes sense that it is slightly higher than 70%. However, since quality standards are set by the manufacturers themselves, they are not notified to KP like this.
According to the standard manufacturing standards for external disinfectants notified by the Ministry of Food and Drug Safety, the content standard for products used directly on the skin, such as hand sanitizers, is set at 54.7-70% (w/w, v/v) if ethanol is the active ingredient.
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| standard manufacturing standards for external disinfectants |
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| Hand sanitizer products labeled with 70% ethanol |
Sterilizers and disinfectants are managed by various ministries depending on their purpose and use. Alcohol-based disinfectants used for surface disinfection are managed by the Ministry of Environment, and the ethanol content is set at 70-90% (set according to ECDC, 2020). The WHO states that maximum effectiveness can be expected up to 60-80%, and 80% ethanol preparations are usually recommended for medical institutions with high risk of infection.
Considering the standards of the Ministry of Environment, WHO, and the standards for external disinfectants of the Ministry of Food and Drug Safety, hand sanitizers are applied to a wide area of the skin, so the minimum concentration is set at 70% or less considering the effect on the skin, and disinfectant alcohol is applied to local areas of the skin or is used for general purposes other than the skin, so it is probably set at 83% v/v. Alcohol swabs are also similar to disinfectant ethanol, although their form is different, so I think the effect is the same.