# Onion (Allium cepa)

**Cepa**

**Known today as.** *Allium cepa*.

Kind: Plant  
Qualities: Hot and dry (Galenic tradition).

## What was it used for?

To ripen boils, provoke urine, and draw the menses; roasted for earache.

## What does modern science say?

Nutritious; no strong medicinal evidence.

## Pharmacognosy and toxicology

- **allyl propyl disulfide**: 
- **syn-propanethial-S-oxide**: the lachrymatory factor
- **quercetin**: up to 50 mg per 100 g in red onions
- **fructans**: 

**Mechanism.** The sulfur compounds inhibit platelet aggregation and are antibacterial; the roasted onion in the ear was a warm poultice; onion extract gel for scars (Mederma) has failed in controlled trials. Onion is toxic to dogs and cats by oxidising their haemoglobin, not to people.

**Dose.** A food.

**Standing.** A food; the German Commission E lists it for appetite and against atherosclerosis on tradition.

## What lore surrounds it?

A widespread modern folk belief holds that a cut onion left in a sickroom, or under the bed or against the feet overnight, draws illness out of the body or the air. It has been traced and debunked repeatedly, and rests on nothing beyond the older, equally unproven idea that onions purify foul air: a living piece of folklore, not a remedy.

## What did the older authorities say?

**Herodotus.** The inscription he reports on the Great Pyramid counted the onions, radishes, and garlic eaten by the workmen.

## Sources

- Herodotus, *Histories* II.
- Snopes, “Do Onions Fight Off the Flu Virus?”
- Blumenthal, M., ed. (1998). *The Complete German Commission E Monographs*, “Onion.”
- Chung, V. Q., et al. (2006). “Onion extract gel versus petrolatum emollient on new surgical scars.” *Dermatologic Surgery* 32.

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*Onion.* In *Materia Medica*, edited by B. C. P. Statema. Version 1, revised 2026-09-25. The Thinking Press. https://thethinkingpress.org/materia-medica/onion

Historical description, not medical advice.