Compounds · Monoterpenes · Terpenoid pathway
α-Terpinene
Faint lemon, thin wood, with a slight herbal note. Less sharp than limonene.
- CAS
- 99-86-5
- Formula
- C10H16
- Molar mass
- 136.23
- Odour threshold
- —
- Boiling point
- ≈ 175 °C at atmospheric pressure
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: ALPHA-TERPINENE.
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.
Why it sits where it does
It has two double bonds in the ring, so it oxidises very easily — one of the terpenes that degrade fastest when an essential oil is exposed to air.
Where else you meet it
Tea tree, cardamom, coriander. In tea tree oil, the share of α-terpinene falls steadily with storage time.