Do hand-washing and gargling really help prevent colds? What is the right way?
This answer is a draft. It stays unpublished until legal review and source verification are complete.
Japanese children are taught at school: "when you come home, wash your hands and gargle" (手洗い・うがい, tearai-ugai). Gargling with plain water as a daily habit barely exists outside Japan, and some newcomers doubt it does anything. Here we separate the evidence for each habit, and the way of doing them that actually works.
Evidence and figures
| Method | Evidence | Guide |
|---|---|---|
| Hand-washing with soap | The most solid evidence for infection prevention. In a Japanese experiment, viruses fell to about 1/100 with running water alone for 15 seconds, and about 1/10,000 with soap for 10 seconds plus running water for 15 seconds (Mori et al., 2006) | Rub for 30 seconds, rinse for 15 seconds |
| Alcohol hand sanitiser | 60–95% ethanol is effective against influenza, COVID-19 and others. Weak against norovirus | A substitute when you cannot wash. Rub in until the hands are dry (about 20 seconds) |
| Water gargling | In a Kyoto University randomised trial (387 people, 2005), the water-gargling group had about 36% fewer colds. The iodine-gargle group showed no significant difference from the control group | When you get home. Rinse the mouth → tilt the head back and gargle for 15 seconds × 2–3 times |
| Masks | The effect of stopping a person with symptoms passing it on is well established. The protective effect for a healthy wearer depends on the situation | Wear one when you have a cough or sneezes |
- Spots most often missed when washing: fingertips and under the nails, between the fingers, the base of the thumb, the wrists. Government awareness material shows these repeatedly as a "missed-spots map".
- When to wash: on getting home, before meals, after the toilet, before and after cooking, after blowing your nose, after touching shared surfaces (train straps, door handles).
- Towels: even at home, one per person, or paper towels. Sharing a damp towel can do more harm than good.
- Gargling cautions: daily use of iodine gargle solution (ヨード液のうがい薬, the brown gargle sold at drugstores) is not recommended (the Kyoto trial showed no benefit, and effects on normal mouth bacteria and on the thyroid have been pointed out). On preventing COVID-19, both gargle makers and the authorities say the evidence is not established.
- Rough hands: apply hand cream after washing. Cracked skin picks up germs more easily and is harder to wash.
[Verify] Check the experimental figures of Mori et al. (2006, Kansenshogaku Zasshi) and the reduction rate in the gargling trial of Satomura et al. (2005, American Journal of Preventive Medicine) against the original papers.
Misunderstanding 1｜A quick rinse under water is enough
Running water alone has about 1/100 of the effect of washing with soap. Soap for 30 seconds, and reach the fingertips, thumbs and wrists.
Misunderstanding 2｜With alcohol sanitiser I do not need to wash
Alcohol works poorly on visible dirt, norovirus and some bacteria. Hand-washing comes first; alcohol is the back-up.
Misunderstanding 3｜Iodine gargle works better than water
In the Japanese trial, water gargling showed a benefit and iodine did not. For everyday gargling, water is enough.
Misunderstanding 4｜Gargling washes viruses out of the throat
Viruses enter the cells within a short time of landing, so the "washing out" effect is limited. Why gargling helps is not fully understood, and regarding it as "a habit on getting home" is the fair position.
Misunderstanding 5｜Hot water washes more germs away
Viruses do not die at temperatures your hands can bear. Hot water only causes rough hands. Use lukewarm or cold water and plenty of soap.
---
Sources
- Ministry of Health, Labour and Welfare, *The right way to wash your hands* [正しい手の洗い方] (awareness material)
https://www.mhlw.go.jp/stf/seisakunitsuite/bunya/0000191947.html
- Mori K. et al., "Effects of hand-washing on removal of virus using feline calicivirus as a surrogate for norovirus" [Norovirusの代替指標としてFeline Calicivirusを用いた手洗いによるウイルス除去効果の検討], Kansenshogaku Zasshi (Journal of the Japanese Association for Infectious Diseases) 80(5), 2006
https://www.jstage.jst.go.jp/article/kansenshogakuzasshi1970/80/5/80_5_496/_article/-char/ja/
- Satomura K, et al. "Prevention of upper respiratory tract infections by gargling: a randomized trial." American Journal of Preventive Medicine, 2005; 29(4): 302–307.
https://doi.org/10.1016/j.amepre.2005.06.013
⚠️ Editorial note: the source URLs above were identified by search. Our working environment cannot reach go.jp domains, so the contents have not been checked against the text. Verify every source before publication and record who checked it and when.
About this article
What we share here are ideas and everyday practices passed down among people living in Japan, together with general information drawn from public sources. They are not official recommendations, and they are not professional instruction. Practices vary between households and regions.
This is general information. Results vary from person to person and depend on your own conditions and surroundings.
Please decide for yourself, using your own judgement, whether any of this suits your situation. We cannot accept responsibility for any damage, loss or injury arising from following this article.
This article is not meant to diagnose or manage any specific medical condition. If you are worried about your health, see a doctor rather than relying on your own judgement.
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