# Citron (Citrus medica)

**Cedro**

**Known today as.** *Citrus medica*, the large thick-rinded ancestor of the lemon.

Kind: Plant  
Poisoning: Phytophotodermatitis (https://thethinkingpress.org/materia-medica/poisons/phototoxic)

## What did Canale use it for?

The seed in purges; the peel in decoctions, pills, and syrup (chs. 4, 6).

## What does modern science say?

Flavor and aroma. No purgative action.

## Pharmacognosy and toxicology

- **limonene**: the peel oil
- **citral**: 
- **bergapten**: 5-methoxypsoralen, a furanocoumarin of the peel
- **hesperidin**: a flavanone

**Mechanism.** The peel oil is carminative and the pith’s pectin is a bulk laxative; the furanocoumarins make the skin burn in sunlight after handling the peel, which is why citrus pickers blister.

**Dose.** Safe as food; the oil on the skin before sun gives phototoxic burns.

**Standing.** A food; no monograph. The related bitter orange peel has an EMA monograph for dyspepsia.

## What lore surrounds it?

Beyond the apothecary, the citron holds a place in Jewish practice of its own: it is the etrog, one of the Four Species held and blessed during Sukkot, a use continuously attested for more than two thousand years.

## What did the older authorities say?

**Pliny.** Calls the citron tree “the Assyrian, and by some the Median apple,” an antidote against poisons, whose fruit “is never eaten” but whose smell is so strong that it penetrates clothes; and later gives citrons, “either the pulp of them or the pips,” taken in wine as an antidote, the juice as a gargle to sweeten the breath, the pips for pregnant women to chew against qualmishness, and the fruit for a weak stomach, “but it is not easy to eat them except with vinegar.”

## Sources

- Pliny the Elder, *Natural History* 12.7, 23.56, trans. J. Bostock & H. T. Riley (1855), Perseus Digital Library.
- Wagner, A. M., et al. (2002). “Bullous phytophotodermatitis associated with high natural concentrations of furanocoumarins in limes.” *American Journal of Contact Dermatitis* 13.
- Lv, X., et al. (2015). “Citrus fruits as a treasure trove of active natural metabolites.” *Chemistry Central Journal* 9.

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

Historical description, not medical advice.