Folk medicine treatment of various skin diseases with oak bark has a tradition. But the drug is increasingly disappearing from the therapeutic repertoire. An orientation to contemporary application and scientific evidence.
The oak species that can be used medicinally are the common oak (Quercus robur L.), the downy oak (Quercus pubescens) and the sessile oak (Quercus petraea) – three species of the genus Quercus from the beech family Fagaceae (Fig. 1). Another important representative is the cork oak (Quercus suber L.). The outer layer of its bark is the cork from which the cork cones are made.
The English oak is the most common in Europe. It is absent only in very warm and dry areas in the south and southwest, and in cooler areas in the north of Europe. Since it needs a lot of light, it is not found in dense forests, but only in light-flooded locations. Oak is in great demand for its valuable wood in the construction industry and for the production of barrels.
Ingredients
In the oak bark is found 10-20% tannins. These are primarily catechins, or more precisely oligomeric proanthocyanidins. These so-called OPCs are dimers or trimers of catechin. The European Pharmacopoeia requires a minimum content of 3% catechins and calculates these as pyrogallol. Other ingredients include ellagitannins, flavanoellagitannins, quercitol and triterpenes.
Folk medicine in use
In Switzerland, apart from anthroposophic remedies, there are no oak preparations approved as medicinal products. In the past, oak bark was also used by traditional medicine, but today it is only occasionally used in folk medicine in the form of baths or poultices. Here it is used for the treatment of inflammatory, non-wetting and small-surface skin rashes. This can also affect the mucous membranes in the anal or genital area and in the mouth. When it comes to lesions in the mouth area, the preparation of oak bark is gargled or brushed. These applications are said to have astringent, antipruritic and antiseptic effects (recommended dosage in the box).
Effect
Due to the astringent ingredients, the effect of which is due to the tannic acid, one can well imagine an effectiveness in certain skin lesions, e.g. hemorrhoids or lesions in the oral mucosa. Tannins may even have antifungal activity, as shown in a recently published pharmacological study [1]. Another study suggests that tannins from the medicinal plant bloodroot (Potentilla officinalis) have an anti-inflammatory effect on atopic skin in the UV erythema test [2].
However, no clinical studies could be found for a documented effect of preparations from oak bark extract with regard to main problems. Oak bark seems to be of too little interest for medical research.
Pharmacological studies
However, some pharmacological studies have been published.
Anti-allergic potential: tannins from English oak appear to have some efficacy against allergy mediators. This was reported in a pharmacological study published in 2016 [3]. For this purpose, the research team chromatographically separated tannins with a high molecular weight from a Quercus robur decoction. Subsequently, the degranulation of activated, allergy-specific basophil cells was measured photometrically. The high molecular weight oak tannins showed a dose-dependent decrease in cell degranulation. This indicates a possible antiallergic activity of these tannins, which at best opens up possibilities for topical treatment of allergies with oak bark extracts.
Wound healing with Quercus infectoria: Gal oak (Quercus infectoria) has been used for medicinal purposes in Asia for a long time, especially for skin problems and wounds. A pharmacological study published in 2017 by a Thai research team documented that extracts from Quercus infectoria have antibacterial and antioxidant activity. For this purpose, wounds were produced on diabetic rats and treated with a gall bladder preparation. Compared with untreated control rats, wound healing improved significantly in treated rats [4].
Cork oak for anti-aging: In 2005, a human in vitro study was conducted in France, which gave a promising result regarding extracts of cork oak [5]. The 15 subjects applied to the forearm either an ointment containing 3% cork oak extract or placebo. After one and after two hours the condition of the skin was examined. In the verum group, some subjects showed a significant decrease in skin roughness after one hour. After two hours, this significant skin change was seen in 78.6%. This study suggests that cork oak extract may increase skin tension and smoothness, which could be used in anti-aging skin care products. And indeed, there are cosmetic products that take advantage of this skin-tightening property of the cork oak.
Summary
Some oak species have a folk medicine tradition, some of them for a long time. Preparations from oak bark are used against various skin and mucous membrane problems as baths, brushings, etc. In Switzerland, except for anthroposophic products, there are no oak bark preparations that have Swissmedic approval. Clinical studies proving dermatological efficacy do not exist. Pharmacological studies and a human in vitro study, on the other hand, concluded that oak bark opens up possibilities in wound healing, allergy control, and skin tightening.
Those who wish to recommend the use of oak bark preparations in their daily practice or receive patient inquiries in this regard can refer patients to a pharmacy that has crushed oak bark in stock and can explain the preparation.
Literature:
- de Freitas ALD, et al: Proanthocyanidin polymeric tannins from Stryphnodendron astringens are effective against Candida spp. isolates and for vaginal candidiasis treatment.
- J Ethnopharmacol 2018; 216: 184-190.
- Hoffmann J, et al: Tannins from Potentilla officinalis display anti-inflammatory effects in the UV erythema test and on atopic skin. J Dtsch Dermatol Ges 2016; 14(9): 917-922.
- Lorenz P, et al: Constituents from oak bark (Quercus robur L.) inhibit degranulation and allergic mediator release from basophils and mast cells in vitro. J Enthnopharmacol 2016; 194: 642-650.
- Chokpaisarn J, et al: Potential wound healing activity of Quercus infectoria formulation in diabetic rats. PeerJ 2017; 5: e3608. doi: 10.7717/peerj.3608.
- Coquet C, et al: Quercus suber cork extract displays a tensor and smoothing effect on human skin: an in vivo study. Drugs Exp Clin Res 2005; 31(3): 89-99.
HAUSARZT PRAXIS 2018; 13(11): 4-5
