# Oak galls

*Oak apples; *gallae**

**Known today as.** Round growths raised on oaks by gall wasps.

Kind: Plant

## What was it used for?

The strongest of astringents, for fluxes, bleeding, and sore gums; and, with iron, the ink of the West.

## What does modern science say?

Rich in tannic acid, genuinely astringent.

## Pharmacognosy and toxicology

- **tannic acid**: up to 70 per cent of the Aleppo gall
- **gallic acid**: 

**Mechanism.** Tannic acid precipitates proteins: it tans leather, inks paper with iron, and tightens tissue, which is the astringent use; given for burns in the 1920s it caused liver damage and was abandoned.

**Dose.** Grams by mouth injure the liver; the burn treatment killed.

**Standing.** Tannic acid survives in a few preparations for cold sores and in the laboratory.

## What lore surrounds it?

Iron-gall ink, made from galls and [vitriol](https://thethinkingpress.org/materia-medica/vitriol), wrote most of the manuscripts of the Middle Ages.

English folk custom read the coming year in them: an oak apple opened on Michaelmas Day that held a worm foretold a pleasant, ordinary year; a spider, shortage and ruined crops; a fly, a moderate season; and nothing at all, the worst sign, serious disease throughout the year.

## What did the older authorities say?

**Pliny.** “All the glandiferous trees produce the gall-nut as well.” The gall-nut of the hemeris oak “is considered the choicest of all, and the best adapted for the preparation of leather,” while the black gall-nut is “deemed preferable for dyeing wool.” Pliny says the gall-nut begins to grow “just as the sun is leaving the sign of Gemini, and always bursts forth in its entirety in a single night”; the white kind grows in a single day and reaches about the size of a bean, the black sometimes “the size of an apple even.” The best come from Commagene, the worst from the robur, and a gall “may easily be tested by means of certain holes in it which admit of the passage of the light.”

## Sources

- Pliny, *Natural History* XVI.
- Dioscorides, *De materia medica*.
- Wikipedia, “Oak apple.”
- Pliny the Elder, *Natural History* 16.9, trans. J. Bostock & H. T. Riley (1855), Perseus Digital Library.
- Wells, D. B., Humphrey, H. D., and Coll, J. J. (1942). “The relation of tannic acid to the liver necrosis occurring in burns.” *New England Journal of Medicine* 226.

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*Oak galls.* In *Materia Medica*, edited by B. C. P. Statema. Version 1, revised 2026-10-01. The Thinking Press. https://thethinkingpress.org/materia-medica/oak-galls

Historical description, not medical advice.