Compounds · Alcohols · Terpenoid pathway
α-Terpineol
Also known as p-Menth-1-en-8-ol — an analysis may use any of these names
Lilac, slightly soapy, soft. One of the molecules that act as connectors and are seldom noticed.
- CAS
- 98-55-5
- Formula
- C10H18O
- Molar mass
- 154.25
- Odour threshold
- 330 ppbin water
- Boiling point
- ≈ 219 °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.
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: TERPINEOL.
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. It is often present in quantity but contributes less smell than its share suggests.
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
The same formula as terpinen-4-ol but with the hydroxyl group in a different position, so it boils ten degrees higher.
The full trio also includes 1,8-cineole, also C₁₀H₁₈O with the same molar mass of 154.25, yet it boils at only 176 degrees — forty-three degrees below this compound. The difference is that cineole hides its oxygen in an ether bridge and cannot form hydrogen bonds, while the other two have an exposed hydroxyl.
Three compounds, one formula, three different positions on the volatility band. It is the clearest example in the library of the position of a functional group mattering more than the elemental composition.
Where else you meet it
Lilac, cardamom, pine. Often an oxidation product of limonene in old citrus oils.