TANE JOURNEY
Who decided
how often we wash?
Five advertisements, and one number
that changed over 50 years
I had trouble with my own skin, and went looking for what would be good for it.
As I looked, I came to know my own assumptions.
What comes easily to mind on hearing the word “wash” ── is that really right?
When was it decided how often we wash? Who decided it?
When I looked into it, the record was still there. One company’s advertisements rewrote that number over 50 years. This is not a guess. It is the wording of the advertisements.
WHAT YOU GET ／ What this page tells you
Three things to take home after reading
There is no need to remember all of it. If one thing stays, that is enough.
- OneWhen, and how, the number of times we wash became what it is now. With the years.
- TwoBeing able to think, just once, “I wonder who looked into this.”
- ThreeHow many times you wash today. It can be counted.
There is only one thing to do first. Count how many times today you washed your hands, face, body, and hair.
Nothing needs to change. Counting is enough.
- 01“Washing” is one word for three things
- 02Five advertisements. Twice a month became every day
- 03What was in the bottle changed around the same time
- 04I wonder who looked into this
- 05Both companies reached the answer that favored themselves
- 06Even so, numbers where both sides pointed the same way
- 07A group average and one person’s body are different things
- 08The words are the ones that remember
- LookWhat to look at when choosing
- TryCount, today
- SourcesWhat this issue is made from
01
“Washing” is one word for three things
Before starting, there is something I want to separate out.
Inside the single word “wash” there are three entirely different things.
- Water onlyRinsing with warm water. Rubbing. Nothing more.
- SoapMade from fats or oils and an alkali. Alkaline, at pH 9–10.
- Synthetic cleansing ingredientsMade from petroleum or from plants. These, too, cannot be treated as one group. The difference between the strong ones and the mild ones is sometimes larger than their difference from soap.
If the three are talked about mixed together, no answer comes out. Among the studies that looked at “what happens to the bacteria on skin when it is washed,” there are some that do not say what it was washed with.
So on this page, the “with what” is always written. When it cannot be written, the page says that it cannot.
This is the first fork in the road. It is not “wash or don’t wash.” With what, and how much ── that is where there is room to choose.
02
Five advertisements. Twice a month became every day
A product was first sold in Japan under the name “shampoo” in 1932 (Showa 7). Around that time, hair was washed once or twice a month.
From there, let us line up the advertisements of one and the same company.
- 1932「せめて月二回は！」 (“At least twice a month!”) ── It is asking.
- 1935「御洗髪は一週一度！」 (“Wash your hair once a week!”) ── It is stating it outright.
- 1965「夏の髪洗いは5日に1度！」 (“In summer, wash your hair once every 5 days!”) ── It is recommending.
- 1976「毎日シャンプーしたっていいんです。」 (“It’s all right to shampoo every day.”) ── It is giving permission.
- 1983「ティーンの2人に1人は毎日シャンプーしてる」 (“One in two teens shampoos every day”) ── A way of saying that everyone is already doing it.
The one line from 1976 says the most
To say “it’s all right to,” there has to have been a “you shouldn’t” before it. The wording of permission is evidence that there was a prohibition.
In other words, as of 1976, washing every day was still “too much.”
Then in 1983 the wording changes. It stops recommending, and becomes “one in two is already doing it.”
When something is recommended, one can decline.
When one feels behind, it is harder to decline.
In 50 years, twice a month became every day. That is roughly 15 times.
In those 50 years, did the human body change? The amount of sweat? The skin?
03
What was in the bottle changed around the same time
This is not only about how often. What we wash with moved in the same period.
In the Showa 30s (1955–64), shampoo in Japan moved from soap to synthetics. Until then it had been soap shampoo. The 1965 “once every 5 days” advertisement came out right in the middle of that shift.
The reason synthetic cleansing ingredients came into being is also on record. Germany, 1916. In the First World War fats and oils ran short, and soap could no longer be made. They were not born for the sake of skin. There was one more circumstance: in hard water, soap leaves scum.
The phrase “gentle on skin” is something that was attached afterwards.
How often and with what did not move separately. They moved together. Thinking about the two apart, it becomes unclear which one is being talked about.
04
I wonder who looked into this
Having come this far, a natural question arises. In the end, what is good to wash with?
There are people who have looked into it. There are papers. But there was something I wanted to look at before that.
One of the most highly regarded kinds of source in medicine is the Cochrane Review. Its work is to gather studies from around the world and compare them. In 2017 it counted 75 studies and more than 8,000 trials, and reported this.
- What was foundResults and conclusions favorable to the company that paid tend to come out more often.
- By how muchRisk ratio 1.27 (95% confidence interval 1.17–1.37).
- Where it entersIn how the question is framed, and in reporting only the convenient results.
- The heaviest partThis bias cannot be found by the usual checks of “study quality.” And the studies funded by companies were, if anything, higher in methodological quality.
The last line is the one that lands.
It looks like a well-made study. Even so, the conclusion leans toward the side that paid. So “because it is a proper study” is not a reason that gets around this bias.
Cochrane itself has published an editorial saying that the source of funding should be included among the items checked.
So at TANE, whenever we look into something, we have decided always to write four things.
Who paid ／ over what period ／ with how many people ／ who gains from the result.
What is not known, we write as “unknown.” Being able to write “unknown” is the more important part.
05
Both companies reached the answer that favored themselves
With that measure in hand, I read two papers comparing soap and synthetics.
- A 2022 reviewWritten by three people in the science division of a company that sells soap-free cleansers. The conclusion: “synthetics are superior.” The paper states “no external funding received” and “no conflicts of interest.”
- A 2025 paperWritten by four people from a company that sells soap, and one from a university. The conclusion: “soap is lower in toxicity and breaks down well.” This one states the name of the company that funded it, and even that it covered the salaries of three of the authors.
Neither is lying. Both have data, and experiments.
But the answer leans just by deciding what to measure. Measure the moisture in skin, or measure what happens after it is washed down the drain. The one who chooses is the one doing the study.
There was something that became visible only when the two were set side by side.
When the synthetics company looked, synthetics came out better.
This is not an accusation. It is a record that such a structure exists. Who is at fault is not written here, because that is not known.
06
Even so, numbers where both sides pointed the same way
Interestingly, there is just one place where things came out pointing the same way seen from both sides. It is not about skin; it is about what happens after it is washed down the drain.
The concentration at which half the fish die
The higher the number, the more has to be put in before they die.
The main ingredient of synthetic detergents (LAS)
mg/L
Soap
mg/L
Soap takes roughly this many times as much
to come to the same result
1 mg/L is 1 milligram in 1 liter of water. Very dilute.
After 28 days, how much has broken down
Soap
% broken down
One synthetic ingredient (SDB)
% ── almost all of it remains
For LAS, there is also a report that at higher concentrations it stops the breakdown process in sewage itself.
There are two things I want to write down honestly here.
One. These numbers for fish and for breakdown come from research by a company that sells soap. The LAS value of 1.67, however, is a value from a document put out by an industry body on the detergent side. So on this point, both sides are pointing the same way.
Two. Soap is not harmless either. Soap scum clogs the gills of fish.
What happens on skin and what happens after it goes down the drain are separate questions. One answer is not enough.
07
A group average and one person’s body are different things
This is the most important caveat on this page.
What research can speak about is what happens when many people are gathered and an average is taken. What happens in your body is a separate matter.
In fact, this is what happened.
- What the research saysThere are reports that synthetic cleansers with a pH brought close to that of skin are less likely than soap to take lipids from the skin’s outer layer (the stratum corneum).
- What happened to meWith one of those said to be “mild,” my skin became dry and rough.
Both are true, and they do not contradict each other.
An average can speak about a group, and it is one person who has a body.
That is why TANE hands over not an answer but what to look at when choosing. That we do not say “this is the right one” is not out of reserve; it is because it cannot be said in the first place.
08
The words are the ones that remember
Before soap, what did people wash with?
Aku (灰汁), lye water. Wood ash is soaked in water and the clear liquid on top is drawn off. That is what they washed with.
And in Japanese, words like these remain.
- 垢抜ける (akanukeru)Said to have come to mean “to become refined” from “the grime (aka, 垢) comes off and one is fresh.” But there is also a theory that this aka is not grime but aku (灰汁), and that the word carried over from akunuki, drawing the harshness out of vegetables. Neither has been settled.
- 足を洗う (ashi o arau, “to wash one’s feet”)Monks walked outside barefoot, and washed their feet before entering the temple. It is said to have included the sense of washing away, along with the dirt, the worldly desires of the outside. That is why “giving up a bad way of living” is said in words about washing a part of the body.
- 禊 (misogi)Said to be a contraction of miso-sogi (身滌). Sosogi is susugi (“rinsing”) with its vowel changed, and susu is said to be a word that copies the sound of water. The sound of water remains inside the word.
- “Cleanliness is next to godliness”The English saying (in Japanese, 清潔は敬神に次ぐ). It is thought to be a line from the Bible, but it is not in the Bible. It is a passage from a sermon of around 1778.
In Japanese and in English alike, “washing” and “rightness” are tied together inside a single phrase.
If the aku theory is true, then the words are the ones that remember the tool. What was used before soap, the words have gone on holding.
WHAT TO LOOK AT ／ Points to look at
Where to look, the next time you read something
Not only about washing. Just three.
- Does it say who paid?If it does, that alone makes it an honest source. When it does not, it is enough to set it down as “unknown.”
- Does it say with what?An account that says only “washing” may have water, soap, and synthetics mixed together.
- When was it, and over how long?That there was no difference over 4 weeks does not mean there is no difference over 30 years. About the longer span, almost nothing is known yet.
What is not known
To write it honestly. What this page has not found an answer to.
- What happens if it is kept up for a long timeOf the long-term effects of how often we wash, researchers themselves write that “almost nothing is known.”
- How long it takes to come backThe time it takes to return to how it was, after the skin’s resident bacteria have been disturbed.
- The relation between lather and the dirt removedNo basis was found for the idea that more lather means more has come off.
- A comparison paid for with independent moneyA study in which someone not on the selling side compared them over a long period with the same measure could not be found.
TRY IT ／ Trying it
Counting, today
Nothing needs to change. Counting is enough.
Hands, face, body, hair. How many times did you wash each of them today?
Of those, how many did you decide for yourself?
If, after counting, there is just one thing you feel like changing, that is enough. How often, or what you use ── either is fine.
Finding what suits you is a matter of trying, and changing again if it was not right, over and over. It can take time. And sometimes, more than one would expect, not doing and taking away matter more.
The things we wash with came into use
only in the last hundred years or so.
Seen from history,
they are the unusual ones
About the body. When changing how often you wash or what you use, go a little at a time, watching how your skin is doing. If dryness, itching, or redness appears, go back. If you have a skin condition, please consult a medical professional rather than deciding on your own.
NEXT ／ What follows
The rest of this, as a booklet too
The same subject, washing, has been put together in a form that can be opened in front of the store shelf. Send the passphrase on LINE, and the full text arrives. It is free.
The passphrase is 洗うこと (arau koto, “washing”)
What this issue is made from
The advertisement wording is from Kao (花王) shampoo advertisements (1932, 1935, 1965), Kao Soft Essential (カオーソフト エッセンシャル; 1976, non-no no. 120), and Essential Cuticle Care (エッセンシャル キューティクル・ケア; 1983).
That hair was washed once or twice a month around 1932, and that the move from soap to synthetics took place in the Showa 30s, are from the company history that Kao has made public.
The source of funding and the leaning of conclusions are from Lundh et al. (Cochrane Database of Systematic Reviews, 2017), which compared 75 studies and more than 8,000 trials.
The two papers comparing soap and synthetics are a review by three members of the science division of Ego Pharmaceuticals (2022), and a paper by four members of Shabondama Soap Co., Ltd. (シャボン玉石けん株式会社) and one other (PLOS One, 2025). How each describes its funding is taken from what the papers themselves state.
The concentration at which half the fish die and the 28-day breakdown rate are from the PLOS One paper above (2025). The 1.67 mg/L for LAS is the value in an OECD document put out by an industry body on the detergent side.
How synthetic cleansing ingredients came into being in Germany in 1916, and the circumstance of hard water, are from several sources on the history of surfactants.
The origins of 垢抜ける (akanukeru), 足を洗う (ashi o arau) and 禊 (misogi) are from entries in Japanese dictionaries and etymological dictionaries. Including the aku theory, all of them are written here as matters on which there are several theories.
That “Cleanliness is next to godliness” comes from a sermon by John Wesley (1778) and is not in the Bible is agreed on across several sources. For the year, however, some give 1791.
What could not be confirmed has been written as not confirmed.