Lemony, rosy, green — like crushed melissa leaves on a warm hand. Citronellal is the aldehyde that defines citronella, but also the chemical precursor to both lily-of-the-valley and menthol.
Fresh, rosy-citrus, green-herbal, with a waxy aldehydic quality. Less piercing than citral, less rounded and sweet than citronellol. The initial impression is a soft lemon zest crossed with the green sap of geranium stems. As the sharp top evaporates, a surprising floral note appears — closer to lily than to rose. On blotter at 10%, the rose-lemon duality is clearest: citronella without the camphoraceous roughness of the crude oil. Substantivity is moderate (approximately 16 hours at 100%), fading cleanly without dissonant oxidation products.
Evolution over time
Immediately
Immediately
Fresh rosy-lemon burst with green-herbal sharpness. Waxy, aldehydic. The citrus and rose facets compete equally.
After a few hours
After a few hours
The citrus top lifts off. A soft, lily-adjacent floral emerges with a clean herbaceous quality. The rose character becomes more apparent.
After a few days
After a few days
Faint sweet-floral trace. Clean fade — no off-notes. Moderate persistence compared to the alcohol citronellol.
Terroir & Expressions
Indicative 2025 wholesale prices.
The Full Story
Citronellal (3,7-dimethyl-6-octenal, CAS 106-23-0) is a monoterpene aldehyde with an unusual dual character: simultaneously citrus and rosy, with a green-herbal undertone. Less sharp than citral, less sweet than citronellol — it occupies the quiet middle ground where lemon meets rose geranium. The scent is waxy and herbaceous at full strength; on dilution, a soft, almost lily-like floral quality emerges.
The molecule dominates Eucalyptus citriodora oil (70–85%) and Java citronella oil (Cymbopogon winterianus, approximately 35%). It also appears in melissa (2–40%, highly variable by chemotype), kaffir lime leaves (up to 80%, predominantly the S-enantiomer), and Ceylon citronella (5–15%). Both enantiomers smell similar; commercial perfumery typically uses the racemic mixture.
What makes citronellal remarkable is its downstream chemistry. Acid-catalyzed cyclization with tin(IV) chloride converts it to isopulegol (85% yield), which is then hydrogenated to menthol. The catalyst work earned Ryoji Noyori the 2001 Nobel Prize in Chemistry.
Separately, hydration of citronellal produces hydroxycitronellal (CAS 107-75-5), the molecule that gave perfumers the ability to recreate lily of the valley — a mute flower that yields no extractable oil. First synthesized in 1905 by Herman Knoll, hydroxycitronellal remains an important synthetic ingredients in muguet accords. One aldehyde, two entirely different olfactory destinations.
Citronellal activates the TRPA1 ion channel in insects, triggering an avoidance response. A 2010 study in Current Biology (Kwon et al.) showed that Drosophila lacking a functional TRPA1 gene could not detect citronellal as a repellent. The same molecule that humans associate with fresh lemon is, for insects, a noxious irritant — the plant's original purpose for producing it was chemical defense, not fragrance.
Extraction & Chemistry
Extraction method: Natural citronellal is isolated from Eucalyptus citriodora oil (70–85% citronellal content) or Java citronella oil (Cymbopogon winterianus, approximately 35%) via fractional distillation. The natural isolate is a racemic mixture (optical rotation -1° to -11°); the synthetic route produces enantiopure material. Both grades are used in perfumery and as intermediates for menthol and hydroxycitronellal manufacturing.
Restricted under IFRA 51st Amendment. Declared fragrance allergen under EU Regulation 2023/1545 (Annex III), requiring labeling above 0.001% in leave-on products and 0.01% in rinse-off products. IFRA use limits range from 0.017% to 2.30% depending on product category.
Synonyms
3,7-dimethyl-6-octenal, citronellal
Physical Properties
Odor Strength
High
Lasting Power
16 hours at 100.00%
Appearance
Colorless to pale yellow clear liquid
Boiling Point
206.00 to 207.00 °C. @ 760.00 mm Hg
Flash Point
169.00 °F. TCC ( 76.11 °C. )
Specific Gravity
0.851 to 0.859 @ 20.00 °C.
Refractive Index
1.446 to 1.453 @ 20.00 °C.
Melting Point
-16.00 °C.
In Perfumery
Citronellal functions as a top-to-heart modifier, providing rosy-citrus freshness with a green-herbal lift. Its dual floral-citrus character makes it useful in both directions: reinforcing lemon accords with a rosy undertone, or giving rose compositions a citrus-green transparency. IFRA restricts it as a sensitizer, with use levels ranging from 0.017% to 2.30% depending on product category. It is a declared fragrance allergen under EU Regulation 2023/1545 (labeling above 0.001% leave-on, 0.01% rinse-off). The molecule's greatest contribution to perfumery is indirect — as the precursor to hydroxycitronellal (CAS 107-75-5), the foundational muguet molecule. Première Peau's Gravitas Capitale uses hydroxycitronellal, the downstream product of this aldehyde, contributing to the composition's citrus-floral bridge.
