Isopulegol and Citronellol in Lemon Eucalyptus Oil

Citronellal is the star of lemon eucalyptus, but it does not perform alone. Tucked just beneath it in published analyses are two quieter molecules, isopulegol and citronellol, and they help explain why this oil smells rounder and greener than a simple lemon.

Lemon Eucalyptus Essential Oil

Our own Lemon Eucalyptus Essential Oil, in sizes from 0.5 oz to bulk.

From $9.99

Shop Now →

What the numbers look like

A good example is the analysis by Miguel and colleagues, who distilled leaves of Corymbia citriodora from a Portuguese arboretum. Their sample showed citronellal at 36%, with isopulegol at 13%, citronellol at 12% and 1,8-cineole at 11%. Treat that as one snapshot, not a standard. A review by Goodine and Oelgemoeller notes that composition shifts with location, season and leaf age, and other sources put citronellal much higher than 36%. When the lead molecule is higher, the others share a smaller remainder. All the sample really shows is that these two supporting players can reach double figures.

You will find the lead molecule's story in our citronellal article; this one is about the supporting cast.

Isopulegol: halfway to menthol

Isopulegol is built from the same ten carbons as citronellal, with the chain closed into a ring. A patent on its manufacture, US7550633, describes making it from citronellal and calls it an important intermediate on the way to menthol, which is produced from it by hydrogenation. That is a nice piece of chemistry to hold in mind when you smell the oil: this molecule sits chemically between a lemon aldehyde and the cooling alcohol of mint.

It is a reasoned link, not a sensory measurement. We describe the oil as lemony, fresh and green, with a crisp, lightly camphorous base, and we would not credit any single molecule for that base. We will say that a hint of coolness underneath the citrus fits what the chemistry would lead you to expect.

One practical wrinkle: industry makes isopulegol deliberately from citronellal, so seeing it on a report does not prove where it came from. In distilled leaf oil it occurs naturally, as the Portuguese sample shows. It is simply a limit of reading a chromatogram, and no accusation against anyone.

Citronellol: the rose side

Citronellol is the floral partner. Wikipedia's entry describes the compound as floral, waxy and rose-like, with the two mirror-image forms leaning toward citronella and leafy notes on one side and rose, geranium and powdery notes on the other. The sources we read do not say which form lemon eucalyptus contains, so this describes the compound, not our oil. It is still a useful picture for blending: if you notice a faint rosy edge, citronellol is a plausible reason, and a floral heart such as lavender, one of the partners we suggest, may meet it there.

Like its big sibling, citronellol is a fragrance material that some people react to. For the isolated compound Wikipedia lists skin irritation, allergic skin reaction and eye irritation hazards, while noting the degree of allergenicity in people is disputed. Together with citronellal's reputation, that is why we say this is an oil for careful dilution. The Tisserand Institute's dilution guidance gives 0.2% to 1% for reactive skin and 0.5% to 1.2% for the face. Our general guidance is 0.5% to 2% with a patch test first, and we would start at the lower end. Our dilution guide and the piece on skin irritation go further.

How to smell for the supporting cast

You do not need a laboratory to enjoy this. Put one drop on a blotter and smell it straight away, then again after a few minutes and after half an hour. The first sniff is the bright, lemony front. Give it time and you may notice the picture soften: a little green, a little cool, perhaps a faint floral edge. Whether you pin those impressions on any particular molecule is up to you. We just think the changing smell is the fun part.

Try the same thing next to a plain lemon, if you have one. The comparison makes the leafy, camphorous side of the oil stand out. Write down what you notice in plain words, since "sunny", "grassy" and "cool" are more useful to a blender than any technical term.

Reading a seller's report with these in mind

If you do get a gas chromatography report, think of isopulegol and citronellol as a consistency check rather than a score. A plausible spread alongside a high citronellal figure, and a batch reference that matches your bottle, is a good sign. A report with no sample details tells you nothing about the bottle in your hand. And even a tidy report has limits: a review of essential oil adulteration points out that dilution with vegetable oil leaves the normalised percentages on such a report unchanged. Our quality guide has the wider checklist.

If your product depends on these numbers, ask us in writing through the contact page before ordering. Wholesale buyers can also start with a sample bottle; see our bulk page.

For most candle, soap and room-spray makers the answer is less technical: smell it on a blotter, test it in your product, and enjoy the fact that a few quiet molecules give a lemon oil its depth. Our scent profile walks through what that smells like.