Compounds · Alcohols · Terpenoid pathway
Menthol
Also known as (−)-Menthol · Hexahydrothymol · Peppermint camphor — an analysis may use any of these names
Peppermint, icy in the nasal cavity. It does not lower the temperature; it only convinces the body that the temperature has dropped.
- CAS
- 89-78-1
- Formula
- C10H20O
- Molar mass
- 156.27
- Odour threshold
- 300 ppbin water
- Boiling point
- ≈ 212 °C at atmospheric pressure
For this compound the two axes sit close together. Volatility tells you whether it leaves a surface early or late; the threshold tells you how much of it the nose needs before it notices.
About the CAS number and optical isomers
The CAS number above is the racemic form. The menthol in natural peppermint oil is the (−) form, l-menthol, and only that form gives the strong cooling sensation — the (+) form is much weaker.
This is the place in this library where the difference between two optical isomers has the clearest practical consequence. Routine gas chromatography cannot tell them apart.
Must be declared on the label
This compound was added by Regulation (EU) 2023/1545 to the list of allergens that must be declared individually on cosmetic labels in the European Union. Name to use on the label: MENTHOL.
The declaration threshold is 0.001% in leave-on products and 0.01% in rinse-off products. This is an EU requirement — see the regulations page for why it matters beyond the EU. This is not legal advice.
Where it comes from
Biosynthetic pathway: Terpenoid pathway — plants build them from identical five-carbon blocks.
About the threshold figure
High if you count smell alone. But most of menthol’s effect goes through cold receptors rather than the nose, so the olfactory threshold does not reflect how strongly it is perceived.
Published thresholds differ by several orders of magnitude, because of differences in measuring method, sample purity and panel. The figure here is an order of magnitude for relative comparison, not a measurement. We give it only for compounds where the literature broadly agrees — 52 of the 106 compounds in the library. The rest are left blank rather than guessed.
Why it sits where it does
A ring alcohol with an exposed hydroxyl group, forming good hydrogen bonds, so it boils at around 212 degrees even though the molecule is not large.
Where else you meet it
Peppermint, medicated balm, rubbing liniments, sweets and toothpaste.