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Absolute ethanol should be diluted before use as sanitizer: Japan manufacturer

Bottles of absolute ethanol, left and isopropyl ethanol disinfectant are seen in this photo taken in Osaka's Kita Ward on April 7, 2020. (Mainichi/Mai Suganuma)

TOKYO -- Amid a shortage of masks and alcohol disinfectant during the novel coronavirus chaos, people are turning to products including ethanol disinfectants and absolute ethanol, usually found in drugstores and other shops.

But unlike the common belief that high concentrations of ethanol mean a better disinfectant, products with low water content reportedly may not have enough sterilizing effect to be effectively used as sanitizers.

Kenei Pharmaceutical Co., a major manufacturer and seller of ethanol products based in the western Japan city of Osaka, told the Mainichi Shimbun how such products should be used.

Alcohol can destroy coronavirus envelope proteins. Therefore, appropriate use of alcohol is said to have a disinfecting effect. Furthermore, ethanol, a type of alcohol, is widely used as a disinfectant and for other purposes.

According to Kenei, ethanol products with around 20% water content work best as disinfectants. This is why Japanese Pharmacopoeia, established by the Ministry of Health, Labor and Welfare to regulate the quality of drugs, requires that ethanol disinfectants have 76.9% to 81.4% ethanol content.

Though it seems that products with a high alcohol concentration are better disinfectants, ethanol is a highly volatile substance, and Kenei says a product with a high concentration will evaporate quickly before doing much sterilizing. For this reason, absolute ethanol, which is required to contain 99.5% or more ethanol, is sold for cleaning electronics that don't go well with water or oil stains seen a lot around the kitchen. Such products are not recommended to be used as hand sanitizers as they may result in injuring the skin.

If diluted, however, the substance can be used as sanitizers, according to Kenei. Absolute ethanol can be diluted to an appropriate alcohol concentration by mixing at about a 4:1 product to water ratio. A Kenei official said, "It's ideal to dilute absolute ethanol with distilled water, but it can be diluted with tap water at home."

Some products are labeled simply "ethanol" without the words "disinfectant" or "absolute," but these contain 95.1% to 96.9% ethanol and also need to be diluted before use on human hands.

The company also sells products called "Disinfectant ethanol IP," including isopropanol, which is also a type of alcohol. Due to the liquor tax, isopropyl alcohol is cheaper than ethanol, and also works as a disinfectant. But compared to ethanol, isopropanol apparently sterilizes fewer varieties of germs, and has a strong degreasing effect, which could lead to dry hands.

Furthermore, Kenei also sells alcohol fuel, but the substance is mainly methyl alcohol, which is poisonous for humans and cannot be used as hand sanitizers. The company warned its customers via its official website in February, saying, "There have been cases in which customers buy it (alcohol fuel) as hand sanitizers by accident."

(Japanese original by Mai Suganuma, Osaka Regional News Department)

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