"Old Person Smell" Is A Real Thing. Here Is The Japanese Persimmon Soap Dermatologists Pointed At.

Nonenal odor starts as early as 40. A regular bar of soap leaves the molecule on the skin. Persimmon tannin is the ingredient dermatologists named.

Sawumi Health Desk

Sat, September 26, 2026 at 9:12 AM · 6 min read

The active is fermented persimmon tannin, pressed into the bar. Fragrance on its own does not do this job.

Wrinkles get the speeches. Hair gets the shelves. The odor that arrives with the same decades gets whispered about, or skipped. It is distinct from ordinary sweat. It shows up on people who already shower. And a standard soap-and-water wash leaves it in place, because the molecule behind it is an oil.

The compound is 2-nonenal. Dermatologists interviewed by HuffPost, Yahoo Health, and BuzzFeed traced the rise to falling antioxidant defenses in the skin, a shift in sebum, and years of oxidative stress. Dr. Sonal Choudhary at the University of Pittsburgh School of Medicine has said the measurable climb starts after 40 and becomes easier to notice in the 50s. The scent itself runs from a light organic note to something mustier, and it varies from person to person. Olfactory adaptation does the rest: the change is gradual enough that the person producing it stops noticing.

The bar

Sawumi persimmon soap

Fermented kakishibu tannin, with green tea

A palm-sized bar for the zones where nonenal collects: the back of the neck, under the arms, the chest, and the feet. One bar lasts about six weeks of daily use.

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Dr. Naana Boakye, founder of Bergen Dermatology, told those reporters that persimmon soap has a plausible mechanism: the tannins bind aldehydes, and the ingredient has a long history of use in Japan. She also said large randomized trials are still missing. She did not endorse a brand. Sawumi is built on the ingredient she described, fermented Japanese persimmon tannin, the extract known as kakishibu, with green tea extract in the same bar.

Cheap bars in this aisle lean on a persimmon scent and a trace of extract. The tannin is the part that costs money. Sawumi is pressed for that tannin, and it is a cosmetic cleanser. It is a wash for the oil. It is not a drug.

Where to use it

Finish the shower on the zones. Thirty seconds of lather is the whole routine.

1. Wash the body the way you already do.
2. Lather the Sawumi bar and work it into the back of the neck, under the arms, across the chest, and over the feet.
3. Behind the ears is the spot people skip and then check with a finger an hour later. Include it.
4. Rinse. On laundry day, wash the pillowcase that has been collecting the oil all week. The skin keeps making it. The cloth keeps a copy until the wash catches up.

What buyers wrote after they switched

Those are buyers of this bar, published on the Sawumi product page. They are individual reports. A granddaughter's comment and a pillowcase after seven days are the checks that match the way the oil actually behaves: slow to notice on yourself, obvious to someone standing close, and stored in fabric.

The rest of the wash

The same tannin shows up in two other Sawumi products for the hours between showers.

Persimmon body wash

The same tannin, in a bottle

For people who want the kakishibu in a wash rather than a bar. Same job: the oil on mature skin, not a perfume layered over it.

See the body wash

Persimmon body wipes

For the car, the bag, the afternoon

Unscented wipes with the persimmon tannin, for the neck, the feet, and the hours when a second shower is not available.

See the wipes

The presence of the odor is a normal biochemical change. Choudhary has compared it with wrinkles and dryness, and she has said thoughtful skin care and proper laundering bring it down. If the pillowcase is the thing that bothers you, the bar is the place to start. The guarantee runs 30 days: email help@sawumi.com and the order is refunded. You do not have to mail the bar back.

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Advertorial for Sawumi. Dermatologists cited here spoke to HuffPost, Yahoo Health, and BuzzFeed. They did not review or endorse Sawumi. Customer lines are published Sawumi reviews. Results vary from person to person. This soap is a cosmetic for external use and is not intended to diagnose, treat, cure, or prevent any disease.