Geraniol

Geraniol is the smell of roses, and of geranium, and of a large share of everything marketed as floral. It is also in citronella, in lemongrass and in palmarosa, which is why it turns up in products that are not trying to smell of flowers at all.

Why it is tested

Geraniol is one of the eight constituents of fragrance mix I, the screening mixture in the European baseline patch test series, tested at 1.0 percent alongside cinnamyl alcohol, cinnamal, hydroxycitronellal, amyl cinnamal, Eugenol, isoeugenol and oakmoss absolute.

The baseline series is built from what actually causes contact allergy rather than from a list of theoretical concerns, so inclusion is a statement about frequency.

Citronellol is its close relative and usually keeps it company in a formula. The two are related closely enough that reacting to one is worth mentioning when the other appears.

The oxidation problem applies here too

Geraniol is a terpene alcohol, and terpene alcohols oxidise when exposed to air and light. The oxidation products are more sensitising than the fresh molecule.

That is the same mechanism as Linalool and Limonene, where the ESCD guideline records that their hydroperoxides “have recently been found to be more common in the younger age groups, which underscores the burden of fragrance sensitization”.

Two consequences follow and neither is on any label. An opened bottle becomes more allergenic over time, and a natural essential oil is a delivery system for the precursor rather than a gentler alternative to a synthetic fragrance.

Where it hides

In anything scented, obviously. Perfume, shampoo, lotion, deodorant.

In products sold as unscented, sometimes, because a masking fragrance is used to cover the smell of raw materials and it is still fragrance.

In insect repellents and candles, through citronella, which is one of the higher-geraniol oils in common use.

In natural and essential-oil products, at higher concentration than in most formulated perfumes.

Reading for it

On a European label geraniol is named at the end of the ingredient list once it passes a threshold, next to limonene and linalool. On an American one the same product may declare the whole scent as fragrance, and there is nothing under that word for anyone to read.

If you suspect fragrance and can find a European version of a product you use, its label carries more. That technique is underused and it is set out on the fragrance allergy page.

Buying around it

Smaller bottles, used faster, kept closed and out of the light. That advice sounds trivial and it is the only intervention available for the oxidation problem, because nothing on the pack records how far along it is.

Reacting to geraniol does not mean reacting to all fragrance. The baseline series tests eight materials separately precisely because reactions are specific, and Balsam of Peru is tested apart from all of them for the same reason.