Educational information, not medical advice — ask your doctor or midwife.
Umbilicaria esculenta is an edible lichen that grows flat on bare rock. It is known as iwatake in Japan and seogi in Korea. A lichen is not one creature: it is a fungus and an alga living as one.
It is first and foremost a food. Cooks soak the dried discs, scrub them, boil them, then use them in soups, vinegared salads and tempura. Dried pieces are sold in East Asian food shops.
Here is the honest verdict on evidence. Human trials are, for practical purposes, absent. Long traditional use tells you that people ate it and valued it; it is not proof that it treats anything, and it is not proof that it is safe in large or concentrated doses.
No one has shown how this lichen acts in the human body. The claims you will read come from lab dishes and from animals.
In test tubes, lichen acids of this group slow the growth of some bacteria. Whether that happens inside a person has not been shown.
Lichen polysaccharides (long chains of sugar) have been given to mice. In those studies they appear to stir immune cells and slow some tumour cells. Mouse results often do not carry over to people.
The lichen is also high in fibre. Fibre adds bulk to stool. That is a food effect, not a drug effect.
Dried whole lichen is the usual form. It looks like a dark, leathery disc with a stubby stalk on the back.
Before cooking it is soaked in water until soft. Grit and the stalk are scrubbed off, and the lichen is boiled. Cooks then add it to soups, salads and fried dishes.
Powders, teas and capsule extracts also exist, but they are uncommon. They are not standardised, so two products can differ a great deal. Their strength in a capsule is far above anything a meal provides.
Umbilicaria esculenta was a prized food in Japan and Korea for centuries. In Japan it is called iwatake, meaning rock mushroom. Gatherers lowered themselves down cliff faces on ropes to cut it free.
It turned up in Edo-period feast cooking and in Korean royal dishes as seogi. Folk sources listed it as a tonic and as something for an upset stomach.
Older Chinese and Japanese texts grouped it with long-life foods. Those writings record what people believed and ate. They were never tests of whether it worked.
Stop eating it and speak to a doctor if you get lasting stomach pain, vomiting or diarrhoea.
Get urgent care for pain in your side or back, or blood in your urine. These can be signs of a kidney stone.
Call emergency services for swelling of the face, lips or throat, or any trouble breathing. That is a severe allergic reaction.
In Japan and Korea it is an ordinary food, sold dried in grocery shops. In the United States and the United Kingdom it is treated as a food or a supplement, and no health claim for it is approved. In the European Union, a concentrated extract could fall under novel food rules.
Evidence grades and traditional-use labels are explained in our methodology. Nothing here is medical advice.
What it is typically used for, usual dose, cautions, and the study behind it where real trial data exists.
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