Yuja in Beauty

Start with the jar. According to the Encyclopedia of Korean Culture, the usual way to make yuja-cha (유자차) is to layer thin slices of the fruit with honey or sugar, keep them in a cool, dry place for two to three weeks, and use the clear syrup that collects, yuja-cheong, stirred into hot water, with pine nuts sometimes floating on top. A quicker version steeps two or three thin slices in hot water, and the peel can also be boiled for a drink. The same entry says the tea has long been thought to ease arthritis and neuralgia, relieve a hangover and help digestion. These are traditional beliefs. Honey-preserved yuja also goes into foods such as yakgwa. For the fruit itself, see yuja, and for its place among winter drinks, traditional Korean teas.

What the old sources say about skin

Nothing, as far as the encyclopedia entries on yuja-cha and the yuja tree show. The tree entry describes the fruit's fragrant rind and a medicinal use of the unripe fruit for nausea, indigestion and the effects of alcohol, but it does not mention a bath or any cosmetic use. The fruit and its peel are valued mainly for aroma and flavor. So yuja in skincare is best read as a modern product idea that borrows a familiar, well-loved fruit.

The yuja bath is Japanese

A reader might expect a Korean winter-solstice yuja bath. The searches behind this page found the custom described only for Japan, where yuzuyu, a bath with whole yuzu floating in it, is taken on the solstice. An English-language Japan-culture site says it was believed to prevent colds and bring good fortune, notes that the earliest known mention is from the Edo period, and adds that claimed benefits such as softer skin and relaxation are not a substitute for medical care. I did not find a Korean source documenting an equivalent bath, so this page does not describe one.

Evidence status

The best-known study is a 2022 paper in Antioxidants on fractions of yuja peel, run entirely in cell cultures: human keratinocytes and dermal fibroblasts exposed to UVB light, and mouse melanoma cells stimulated to make pigment. Treated cells showed lower levels of collagen-degrading enzymes, restored hyaluronic acid and moisturizing-factor expression, and made less melanin. The authors said the fractions showed anti-wrinkle, moisturizing and whitening effects at low toxicity in these tests. The paper has limits worth stating plainly: no animal or human data, two of the cell lines are immortalized or cancer-derived, and the active compounds were assumed from their polarity and earlier reports rather than measured. In my searches I did not find a published human trial of yuja extract for wrinkles or hydration.

Bottom line

• Table: well documented. Yuja-cheong tea is a Korean winter staple, and it is sweet; see sugar in Korean food.
• Traditional beauty use: not documented in the Korean encyclopedia sources reviewed; the bath is a Japanese custom.
• Topical evidence: early laboratory work on peel fractions only.
• Practical note: as with any new product, patch testing is sensible, and people allergic to citrus should take care with both the tea and cosmetics.