Naringenin

Naringenin is a flavonoid found in citrus fruit, particularly grapefruit, where it contributes to the bitter taste. In cosmetics it appears as an isolated compound rather than as a citrus extract, and that distinction is the most useful thing about it.

Isolated compound versus botanical extract

Most plant-derived ingredients on a label are extracts: "grapefruit fruit extract," "green tea leaf extract." The INCI name tells you the plant and the part used, and nothing about what is actually in the bottle. Extraction method, solvent and active concentration all vary enormously between suppliers, and none of it appears on the label.

An isolated compound is different. Naringenin is a single defined molecule with a known structure, present at a known purity. Comparing two products containing naringenin is meaningful in a way that comparing two products containing grapefruit extract is not.

There is a second consequence. Citrus oils raise questions about phototoxicity, because expressed peel oils contain furocoumarins, and about fragrance allergens such as limonene and citral. Naringenin carries none of that. It is not an oil, has no scent, and contains no furocoumarins.

This is why formulations aimed at sensitive or recently treated skin often use isolated flavonoids where a citrus extract would be unsuitable.

How it works

Naringenin is a potent free radical scavenger, and research also reports anti-inflammatory activity through effects on inflammatory signalling pathways.

Work has additionally examined its effects on tyrosinase, the enzyme initiating melanin production, and on UV-induced damage, though the topical skin research is considerably less developed than the general pharmacological literature.

Naringenin and naringin

Two related compounds worth distinguishing. Naringin is the glycoside, naringenin with a sugar attached. Naringenin is the aglycone, the sugar-free form.

Naringenin is smaller and more lipophilic, which suits it better to topical use. Naringin is the form more often discussed in nutrition research.

The grapefruit drug interaction

Worth addressing since it is well known and causes reasonable questions.

Grapefruit juice interferes with the metabolism of many medications by inhibiting an enzyme in the gut and liver. That effect is attributed principally to furanocoumarins, and to some extent to flavonoids including naringin.

It is a consequence of drinking grapefruit juice, not of applying a flavonoid to skin. Topical naringenin at cosmetic concentrations does not produce systemic exposure comparable to ingestion, and there is no established interaction concern.

In formulation

Oil-soluble, stable, and used at low concentrations. Its lipophilicity suits it to anhydrous and oil-phase formulations, where a water-soluble antioxidant would not disperse.