Educational information, not medical advice — ask your doctor or midwife.
Cork oak (Quercus suber) is an evergreen oak tree of Portugal, Spain and north-west Africa. Its thick, spongy outer bark is stripped every nine years or so to make cork. In Portugal it is called sobreiro, and in Spain alcornoque.
As a folk remedy, the useful part was never the cork itself. Country people used the astringent inner bark, and sometimes the acorns. Bark water was used as a gargle, a skin wash or a sitz bath.
The honest verdict: there is almost no human evidence for cork oak as a medicine. The tree is studied as a crop and a material, not as a treatment. Long folk use is not proof that it works, and not proof that it is safe.
The old idea rests on tannins, the bitter plant chemicals that make oak bark pucker your mouth.
In test tubes, tannins bind to proteins. This makes the top layer of skin or gum tissue tighter and drier. That drying effect is what folk healers meant by an "astringent".
Lab work on oak barks also reports antioxidant activity. Some extracts slow the growth of certain bacteria and fungi in a dish. Whether any of that happens on human skin or in the gut is not established.
For diarrhoea, the proposed action is local. Tannins may tighten the gut lining and bind fluid, so stools firm up. This has not been tested in people using Quercus suber.
No trial has shown that cork oak treats any condition. Treat the mechanism as a reasonable idea, not a proven effect.
Cork oak is rarely sold as a remedy. Most of what you can buy is cork as a material, or oak extracts used as food and drink flavouring.
The traditional forms were simple ones.
Bark decoction: inner bark simmered in water, cooled, then used as a gargle or skin wash.
Sitz bath: the same bark water added to a shallow bath.
Bark powder: dried bark ground fine and dusted on damp skin.
Roasted acorns: ground and brewed as a coffee-like drink in lean years.
Cork goods: stoppers, flooring, boards and fabric. These are materials, not medicines.
Standardised cork oak capsules or tinctures are not a normal shop item. Where "oak bark" is sold in Europe, it is usually Quercus robur or Quercus petraea, a different species with its own label rules.
Cork oak sat at the centre of rural life in Portugal, Spain and parts of Italy and north Africa. Farmers valued it for cork, charcoal, shade and pig feed, long before anyone used it as a remedy.
Folk healers treated the inner bark as a drying, tightening agent. Bark water was used as a mouth rinse for sore gums, a wash for weeping rashes, and a sitz bath for piles. Some households also used it for loose bowels.
Acorns were famine food. They were leached, roasted and ground into flour or a coffee substitute.
These uses were recorded by folklorists, not tested by researchers. Nothing here is an endorsement of trying them yourself.
Stop and see a doctor if you get belly pain, vomiting, or a rash after using it.
Get medical help the same day if you notice dark urine, yellow skin or eyes, or you pass much less urine than usual.
See a doctor rather than treating yourself if diarrhoea lasts more than two days, if there is blood in the stool, or if a child or an older adult is becoming dry and drowsy.
Call emergency services for swelling of the lips, tongue or throat, or trouble breathing.
In the European Union, cork oak is a protected farm and forestry tree, and cork is approved as a food contact material. Cork oak bark is not a licensed herbal medicine anywhere; the oak bark approved by the European Medicines Agency for traditional use is Quercus robur, petraea or pubescens. In the United States it is not an approved drug, and no established supplement category covers it.
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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