Where is Citral found?

In this library, Citral contributes to the smell of bruised lemongrass, Vietnamese lime peel.

What is the boiling point of Citral?

About 229 °C — medium, the body of the smell.

What is the odour threshold of Citral?

30 parts per billion in water — the lowest concentration at which the human nose still detects a smell.

Compounds · Aldehydes · Terpenoid pathway

Citral

Also known as Lemonal · 3,7-Dimethyl-2,6-octadienal — an analysis may use any of these names

Sharp lemon with body, slightly harsh. This is the lemon smell the food industry uses, not the smell of real lemon peel.

CAS: 5392-40-5
Formula: C₁₀H₁₆O
Molar mass: 152.23
Odour threshold: 30 ppbin water
Boiling point: ≈ 229 °C at atmospheric pressure

Volatility

150 °C290 °C

Threshold

most potentleast potent

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.

Where it occurs

Each bar spans the lowest to the highest value measured across published lots. The dot is the mean. A wide range is not an error — it is the mark of a natural raw material.

0 7 13 20 %

Cold-pressed lemon peel 1 lot

2.3–2.3
mean 2.3

Must be declared on the label

This compound is on the list of allergens that must be declared individually on cosmetic labels in the European Union, as one of the 24 substances listed before Regulation 2023/1545. Name to use on the label: CITRAL.

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

Moderate. Lemongrass contains citral at such high concentration that it far exceeds the threshold, which is why it arrives in the first second even though it boils at 229 degrees.

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

Citral is not one compound but the common name for a mixture of two geometric isomers: geranial, the (E) form, and neral, the (Z) form. They have the same formula and the same mass, differing only in the orientation of one double bond.

An unsaturated aldehyde with a double bond conjugated to the carbonyl group, so the molecule is more stable and boils higher than saturated aldehydes of the same size. The 229 degrees given here is the boiling point of geranial, usually the dominant component; neral boils about two degrees lower.

On an analysis that separates them, you will see two peaks close together rather than one. If an analysis gives a single line for citral, it is combining two compounds — and the ratio between them is information lost.

Where else you meet it

Lemongrass, lemon peel, ginger, and almost every artificial lemon flavour in the food industry.

Dictionary entries that mention this compound

Reading the table above correctly

Percentage is not odour strength. The human nose’s detection thresholds differ by up to millions of times from one compound to another.

A wide range is normal. A supplier who publishes identical figures year after year is something to question, not something to trust.