Oak Galls (Quercus infectoria, Manjakani) in Women's Intimate Health: A Critical Review of the Clinical Evidence, Effects on the Vaginal Ecosystem and Safety

1. Introduction

Galls of Quercus infectoria and related oak species are abnormal outgrowths formed in response to gall wasps, and are among the richest natural sources of hydrolysable tannins. They have a long history of use in Persian, Unani, Chinese and Malay medicine, particularly for women. Traditional texts recommend them for vaginal discharge, uterovaginal prolapse and vaginal laxity [1], and they are used in postpartum care [2]. In Malaysia, where the galls are known as manjakani [3], they are also common ingredients of feminine washes and of products marketed for vaginal tightening.

A 2023 systematic review by Banc and colleagues summarised the phytochemistry and biological activities of oak galls reported between 2018 and 2023, covering antioxidant, anti-inflammatory, antimicrobial, tissue-protective, antitumour and hypoglycaemic effects, and concluded that preclinical findings should be confirmed clinically with attention to safety [2]. That review did not discuss gynaecological or intimate uses, although these are the main consumer applications of oak galls in Southeast Asia. A 2020 review described the traditional gynaecological uses but predated recent evidence on the vaginal ecosystem and intravaginal practices [1].

This review addresses that gap. It examines the clinical evidence for oak gall preparations in female genital conditions, their probable effects on the vaginal microbiota, their safety by route of use, and the analytical quality of the composition data on which product dosing depends.

2. Methods

Europe PMC and Crossref were searched to October 2026 for clinical, in vitro and toxicological studies of Quercus galls in female genital conditions, and for epidemiological studies of intravaginal practices and the vaginal microbiota. The reference lists of the 2023 systematic review [2], a review of oak galls in female genital disorders [1] and a 2026 review of intravaginal herbal formulations [4] were screened. Composition data reported in the 2023 review were checked against the original studies. Studies were appraised narratively for design, comparator, outcome timing and applicability to commercial products. No pooled analysis was attempted.

3. Composition and Its Measurement

Oak galls are dominated by gallotannins, with gallic and ellagic acids, small amounts of flavonoids and other phenolics [2]. Product doses are therefore usually expressed in terms of tannin or tannic acid content. Several values compiled in the 2023 review cannot be correct as mass fractions. A study of ultrasound-assisted extraction with ionic liquids reported tannic acid yields of 1556 to 2430 mg per gram [5], and a study of manjakani decoction reported 2234 mg per gram [3]; both exceed the mass of the material itself. Such values arise when tannin is measured by colorimetric reactions and expressed as tannic acid equivalents, or when calibration and dilution are not controlled. The 2023 review also listed hypericin, pseudohypericin and hyperforin, compounds characteristic of Hypericum species, among the constituents of oak galls, apparently from a study in which these were included in the panel of reference standards [2,6]. Their presence in Quercus galls has not been established.

These problems matter for products. A dose expressed as milligrams of tannic acid equivalents is not comparable between laboratories, and impossible values cannot support specifications. Oak gall extracts intended for products should be standardised by validated chromatography of named gallotannins and gallic acid, with results that sum to less than the mass of the extract.

4. Clinical Evidence in Genital Conditions

Three clinical studies of oak gall preparations in female genital conditions were identified (Table 1). The most informative is a double-blind randomised trial in 84 women with bacterial vaginosis, which compared a vaginal cream containing a methanol extract of oak gall with metronidazole vaginal gel, each used for 5 days [7]. Cure was reported in 82.1% of the oak gall group and 87.5% of the metronidazole group (p = 0.56). The authors concluded that oak gall was as effective and safe as metronidazole. A non-significant difference in a trial of this size does not establish equivalence. The trial was not designed with a non-inferiority margin, and with about 40 women per arm the 95% confidence interval for the difference extends to a disadvantage of roughly 20 percentage points for oak gall. Cure was assessed only 4 to 7 days after treatment, whereas bacterial vaginosis commonly recurs within months, and the composition of the cream was not standardised to a named marker.

A placebo-controlled trial tested a vaginal cream of a different species, Quercus brantii [8], and a trial in uterovaginal prolapse was published in a journal outside the indexed medical literature [9]; neither could be verified in detail. No trial was found that tested oak gall products for vaginal laxity or tightening with any objective or validated outcome. A 2026 review of intravaginal herbal formulations similarly found that most evidence for herbal vaginal preparations comes from small trials with short follow-up [4]. The clinical case for oak gall in bacterial vaginosis is therefore preliminary, and the case for tightening is absent.

5. Effects on the Vaginal Ecosystem

A healthy vaginal microbiota in women of reproductive age is usually dominated by Lactobacillus species, which maintain a low pH through lactic acid production; communities depleted of lactobacilli and rich in anaerobes are associated with bacterial vaginosis [10]. Any product applied repeatedly to the vagina should therefore be judged by its effect on lactobacilli as well as on pathogens.

The antimicrobial activity of oak gall is broad. Gall extracts inhibited five Candida species [11] and a wide range of bacteria [2]. In the only study identified that tested a Lactobacillus species, a methanol extract inhibited Lactobacillus acidophilus at minimum inhibitory concentrations of 0.16 to 0.31 mg/mL, the same range as for Staphylococcus aureus and Candida albicans [2,12]. That strain was tested as an oral cariogenic organism rather than a vaginal isolate, and the dominant vaginal species such as L. crispatus and L. iners have not been tested. The available data nevertheless give no reason to expect that oak gall spares protective lactobacilli.

Epidemiological evidence on intravaginal practices points the same way (Table 2). In a prospective study of 3620 women, regular douching increased the risk of bacterial vaginosis by about 21% after accounting for women who douched because of symptoms [13]. In an individual participant data meta-analysis of 14,874 women in sub-Saharan Africa, insertion of products to dry or tighten the vagina was associated with HIV acquisition (adjusted hazard ratio 1.31, 95% confidence interval 1.00 to 1.71), and intravaginal cleaning with soap was associated with the development of disturbed vaginal flora [14]. Intravaginal practices are common in Southeast Asia, motivated largely by ideas of femininity and health [15], and their biological consequences are plausibly mediated by disruption of the vaginal flora [16]. Oak gall products marketed for tightening are astringent intravaginal products of exactly the type these studies describe. None of these studies tested oak gall specifically, so the risk is inferred rather than demonstrated, but the burden of proof should lie with products intended for repeated intravaginal use.

6. Systemic Safety

6.1. Oral Use

The 2023 review concluded that aqueous oak gall extracts showed no evident toxicity in rodents [2]. The most detailed repeated-dose study tells a more cautious story. In female rats given a hydroalcoholic extract of Q. brantii galls for 28 days, a single dose of 2000 mg/kg caused no deaths, but 500 and 1000 mg/kg/day produced microscopic lesions in the liver, kidney, stomach, heart, spleen, lung, uterus and ovary, raised thyroid-stimulating hormone and lowered triiodothyronine and thyroxine; 50 mg/kg/day had no effect [17]. Converting the no-effect dose to a human-equivalent dose by body surface area gives about 8 mg/kg, or roughly 480 mg/day for a 60 kg adult, and the conventional 10-fold safety factor would reduce this to about 50 mg/day [20]. These figures apply to one extract of one species and are not a recommended dose, but they show that oral doses of several grams of gall extract, as found in some traditional preparations, are not supported by the toxicology.

6.2. Mucosal and Damaged Tissue

Tannic acid is poorly absorbed through intact skin and gut, but it is absorbed through damaged tissue. In the 1940s, tannic acid applied to burns was linked to liver necrosis [18], and tannic acid added to barium enemas, which contact the colonic mucosa, was associated with deaths attributed to absorbed tannic acid, and its use was subsequently reviewed [19,21]. These historical observations are directly relevant to the traditional postpartum use of manjakani, when the vaginal and perineal tissues may be torn or sutured. Products should not be applied to broken or healing tissue until absorption and wound-healing data are available.

6.3. Pregnancy

No study of oak gall safety in pregnancy was identified. Because gall preparations are used around childbirth and contain high concentrations of tannins with antimicrobial and protein-precipitating activity, use in pregnancy should be avoided until data are available.

7. Implications

7.1. For Products and Claims

The evidence supports different positions for different routes (Table 3). External washes for the vulva carry the least concern but no therapeutic evidence. Intravaginal creams for bacterial vaginosis are investigational and should be used, if at all, under medical supervision. Products marketed for vaginal tightening have no supporting trials and belong to a category of intravaginal practice that has been associated with harm. Oral supplements need doses justified from repeated-dose toxicology. All products should be standardised by validated chromatography rather than tannic acid equivalents, and claims should be limited to what the evidence supports.

7.2. For Research

Four studies would change the evidence base. The first is an in vitro study comparing the activity of standardised gall extracts against vaginal isolates of L. crispatus, L. iners and L. gasseri with that against Gardnerella vaginalis and Candida species, which would show whether a selective concentration window exists. The second is a mucosal irritation study in a validated model, measuring epithelial integrity and inflammatory markers. The third is a randomised trial in bacterial vaginosis with a prespecified non-inferiority margin, standardised product, microbiota sequencing and follow-up for recurrence at three and six months. The fourth, if tightening claims are to continue, is a trial using validated measures of vaginal laxity and sexual function, with assessment of mucosal integrity.

7.3. Limitations

This review is narrative. Two clinical studies could not be examined in full, and the in vitro evidence on lactobacilli comes from a single non-vaginal strain. The epidemiological studies of intravaginal practices did not test oak gall products specifically and were conducted mainly outside Southeast Asia. The toxicological study used Q. brantii rather than Q. infectoria. The author's company manufactures botanical extracts and women's health products.

8. Conclusions

The 2023 systematic review established that oak galls are rich in gallotannins with broad biological activity, but did not address their main consumer use in women's intimate care. One small trial suggests short-term benefit in bacterial vaginosis without establishing equivalence to standard treatment, and no trial supports tightening claims. Gall extracts inhibit lactobacilli as readily as pathogens, intravaginal douching and tightening practices carry epidemiological risk signals, repeated oral dosing has caused organ and thyroid effects in rats, and tannic acid can be absorbed through damaged tissue with serious consequences. Some published composition data are physically impossible. Until data on the vaginal microbiota, mucosal irritation and recurrence are available, oak gall products should be limited to external use, avoided in pregnancy and on damaged tissue, standardised by validated chromatography, and marketed without therapeutic or tightening claims.