Meet the food

A bulb, not a root.

The common onion is Allium cepa, a member of the Amaryllidaceae family. The layered bulb is the familiar food; the roots grow beneath it. Red, yellow and white market onions belong in this food conversation, while a prepared onion extract is a different material. [1]

Raw slices contribute crunch and sharpness; roasted onion can become part of a blended soup, while chopped onion distributes through a hash. These preparations create different eating experiences without requiring a health claim to explain their value.

The cutting-board chemistry

Why a fresh cut can bring tears.

Chopping an onion sets off chemistry that produces a volatile, eye-irritating lachrymatory factor. A 2002 research report identified lachrymatory-factor synthase as an enzyme required for its production, rather than treating that step as a spontaneous reaction alone. [2]

This is a useful distinction: the substance that makes your eyes water is not the same thing as the flavonoid quercetin. A strong aroma does not tell you how much quercetin an onion contains.

What the food contributes

A portion matters more than a superfood label.

FDA's raw-vegetable reference lists a 148 g medium onion with approximately 45 calories, 11 g carbohydrate and 3 g dietary fiber. Those are rounded reference values for a whole raw portion, not for a spoonful of garnish or an onion cooked with oil. [3]

Onions also contain quercetin glycosides: quercetin molecules with attached sugar groups. In a 2001 food-composition study, two prominent forms were quercetin glucoside and quercetin diglucoside. The sugar attachments are part of these molecules; they do not make quercetin a vitamin or turn it into ordinary table sugar. [4]

Original food research

Cooking changes more than texture.

The 2001 experiment found that boiling moved some quercetin glycosides into the cooking water, with about a 30% decrease in the onion under its tested conditions. That is movement between food and water, not necessarily complete destruction of the compounds. [4]

A 2021 study compared yellow- and red-skinned onions after baking, boiling, frying and grilling, then used a laboratory digestion model. Baking gave the highest amount of bioaccessible phenolic compounds in both varieties after simulated digestion. [5]

Across the skincare label

Onion food is not onion-extract gel.

Allium Cepa Bulb Extract is a separate cosmetic INCI for a solvent extract, with a listed skin-conditioning function. The name alone does not specify the solvent, extract concentration or finished formula. [6]

This result applies to those preparations and surgical scars. It is not a test of eating onions, a reason to apply kitchen onion to a wound, or proof that all onion-containing products behave identically.

At home

Store the whole bulb differently from a cut one.

Whole onions are kept in a cool, dark, ventilated place. Cut onion instead belongs in a tightly sealed refrigerated container; Iowa State’s guidance is to use it within seven days. Rinse before preparation. [8]