Definition
Hydroxycitronellal is a synthetic aromatic compound belonging to the class of oxygenated terpenic aldehydes. It is widely used in perfumery and cosmetics for its fresh, floral, and sweet lily-of-the-valley-like scent.

It does not occur naturally in pure form and is manufactured through chemical synthesis.

1. Chemical structure

• IUPAC name: 7-hydroxy-3,7-dimethyloctanal

• Molecular formula: C₁₀H₂₀O₂

• Molar mass: 172.26 g/mol

• Chemical class: oxygenated aliphatic aldehyde

• Functional groups: aldehyde (-CHO) and hydroxyl (-OH)

• Appearance: clear, colorless to pale yellow liquid

• Boiling point: ~250 °C

• Solubility: slightly soluble in water, soluble in alcohols and oils

• Odor: fresh, floral, sweet, resembling lily of the valley

2. Main constituents

Hydroxycitronellal is a pure compound, but in commercial fragrance blends, it may appear alongside or be formulated with other aroma molecules such as:

• Benzyl alcohol

• Linalool

• Citronellol

• Geraniol

• Other minor terpenic alcohols and aldehydes

These may serve as co-formulants to support or complement its floral character.

3. Production or extraction method

Hydroxycitronellal is produced industrially via synthetic methods, typically in the following way:

• Starting material: Citronellal (obtained by fractional distillation from citronella oil or chemical synthesis)

• Reaction:

  • selective hydration of the double bond in citronellal to introduce a hydroxyl group

  • partial oxidation under controlled conditions

• Purification: achieved by fractional distillation or selective crystallization

This process yields a stable product with a high content of the desired isomer with consistent olfactory performance.

4. Olfactory properties

• Main note: floral, fresh, sweet

• Olfactory reference: lily of the valley

• Fragrance family: floral–aldehydic

• Persistence: moderate

• Usage: typically a heart note in perfume compositions

5. Applications

Cosmetic and fragrance industry

• Perfumes (especially floral and green floral accords)

• Creams and lotions

• Deodorants and skin care products

• Shampoos, conditioners

• Soaps and detergents

• Home care: fabric softeners, air fresheners

INCI Functions:

Perfuming. Unlike fragrance, which can also contain slightly less pleasant or characteristic odours, the term perfume indicates only very pleasant fragrances. Used for perfumes and aromatic raw materials.

Cosmetic Safety

Restricted cosmetic ingredient as III/72  a Relevant Item in the Annexes of the European Cosmetics Regulation (EU) 2023/1545. Substance or ingredient reported: Hydroxycitronellal

Product Type, body parts    (a) Oral products (b) Other products

Maximum concentration in ready for use preparation    (b) 1,0 %

Other    (a) (b) The presence of the substance must be indicated in the list of ingredients referred to in Article 19(1)(g) when its concentration exceeds: — 0,001 % in leave-on products — 0,01 % in rinse-off products

Aroma industry

• Used to reconstruct the scent of lily of the valley, which cannot be extracted naturally

• Common in floral and spring-themed compositions

6. Safety and regulations

• IFRA (International Fragrance Association): sets strict concentration limits in cosmetics due to potential for skin sensitization

• EU Cosmetic Regulation 1223/2009 – Annex III:

  • must be declared on labels if concentrations exceed:

    • 0.001% in leave-on products

    • 0.01% in rinse-off products

• Identified as a potential allergen via dermatological patch tests

• Not classified as carcinogenic, mutagenic, or toxic to reproduction

• At normal use levels, it is considered safe, though highly concentrated forms may cause skin irritation or allergic contact dermatitis

7. Conclusion

Hydroxycitronellal is a synthetic fragrance material with a soft, floral-lily note, widely appreciated for its ability to impart freshness and delicacy to a fragrance blend. Though synthetic, it is a cornerstone of modern perfumery used to recreate olfactory effects that cannot be derived from nature.

Its use is well regulated, and with proper labeling and formulation, it remains a safe and valuable aromatic component in cosmetics and personal care.

Comparative Profile: Hydroxycitronellal vs Lyral vs Lilial

Regulatory overview: fragrance allergens (EU + IFRA)

EU Regulation 1223/2009 – Annex III

• Lists 26 fragrance allergens (soon to be expanded to 80+) that must be declared on cosmetic labels if present above:

  • 0.001% in leave-on products

  • 0.01% in rinse-off products

• These include:

  • Hydroxycitronellal, Linalool, Geraniol, Citral, Coumarin, Eugenol, etc.

• These ingredients are not banned, but restricted and labeled for consumer awareness and allergy prevention.

Annex II – Prohibited substances

• Some substances are completely banned due to high risk (e.g., mutagenicity, carcinogenicity, reproductive toxicity):

  • Lyral (entry 1666): prohibited due to strong allergenic potential

  • Lilial (entry 1669): banned because of classification as CMR 1B (toxic for reproduction)

IFRA Standards (International Fragrance Association)

• IFRA imposes concentration limits or outright bans based on toxicological review:

  • Hydroxycitronellal: restricted by product category

  • Lyral and Lilial: prohibited in all fragrance products due to high risk

• Compliance with IFRA standards is voluntary but widely adopted by responsible manufacturers and brands

References__________________________________________________________________________

Svedman C, Bruze M, Johansen JD, Andersen KE, Goossens A, Frosch PJ, Lepoittevin JP, Rastogi S, White IR, Menné T. Deodorants: an experimental provocation study with hydroxycitronellal. Contact Dermatitis. 2003 Apr;48(4):217-23. doi: 10.1034/j.1600-0536.2003.00094.x. 

Abstract. Axillary dermatitis is a common problem, particularly in individuals with contact allergy to fragrances. Many individuals suspect their deodorant to be the causal product of their fragrance allergy. It has been shown that deodorants containing cinnamic aldehyde (cinnamal) can elicit axillary dermatitis in patients sensitized to this substance. The aim of the present investigation was to evaluate the importance of hydroxycitronellal used in deodorants for the development of axillary dermatitis, when applied by individuals with and without contact allergy to this fragrance chemical. Patch tests with deodorants and ethanolic solutions containing hydroxycitronellal, as well as repeated open application tests (ROAT) with roll-on deodorants with and without hydroxycitronellal at different concentrations, were performed in 14 dermatitis patients, 7 with and 7 without contact allergy to hydroxycitronellal. A positive ROAT was noted only in the patients hypersensitive to hydroxycitronellal (P < 0.001) and only in the axilla to which the deodorants containing hydroxycitronellal had been applied (P < 0.001). Deodorants containing hydroxycitronellal in the concentration range of 0.032-0.32% used twice daily on healthy skin in individuals hypersensitive to hydroxycitronellal can elicit axillary dermatitis in a few weeks.

Heydorn S, Andersen KE, Johansen JD, Menné T. A stronger patch test elicitation reaction to the allergen hydroxycitronellal plus the irritant sodium lauryl sulfate. Contact Dermatitis. 2003 Sep;49(3):133-9. doi: 10.1111/j.0105-1873.2003.00175.x.

Abstract. Household and cleaning products often contain both allergens and irritants. The aim of this double-blinded, randomized, paired study was to determine whether patch testing with an allergen (hydroxycitronellal) combined with an irritant [sodium lauryl sulfate (SLS)] cause a stronger patch test elicitation reaction than patch testing with the allergen (hydroxycitronellal) alone, in patients previously patch tested positive to hydroxycitronellal. A stronger patch test elicitation reaction was defined as at least 1 day of patch test reading showing more positive patch tests (+, ++ or +++) on the forearm patch tested with 6 concentrations of SLS plus hydroxycitronellal than on the forearm tested with 6 concentrations of hydroxycitronellal alone and no day of patch test readings showing more positive tests on the hydroxycitronellal forearm. 15/20 (75%) had at least 1 day of patch test reading with more positive patch tests on the forearm patch tested with SLS plus hydroxycitronellal and no day of patch test readings with more positive patch tests on the forearm tested with hydroxycitronellal (P = 0.0253). Estimation of the blood flow with laser Doppler supported these findings.

Ford RA, Api AM, Suskind RR. Allergic contact sensitization potential of hydroxycitronellal in humans. Food Chem Toxicol. 1988 Nov-Dec;26(11-12):921-6.

Abstract. Hydroxycitronellal, an important ingredient in fragrances, was studied for its sensitizing potential in human skin. Fifteen human maximization tests were conducted with hydroxycitronellal obtained from four different sources at induction concentrations from 5 to 12%. No reactions were induced at 5% in two separate panels while 10% sensitized 2/25 panelists in one test but none in a second. Induction at 12% produced sensitization in 8 of 11 tests. Impurities do not appear to be a sensitizing factor. There is some evidence that the l-stereoisomer is a less potent sensitizer than the d-stereoisomer. In an initial modified human repeat-insult patch-test two positive reactions to challenge were observed among 197 panelists, one at a concentration of 5% and the other at 7.5%. When 100 of the non-reacting panelists were re-exposed in the same way, allergic sensitization reactions appeared during the induction period with concentrations as low as 2.5%. When 28 sensitized panelists were exposed to 1% concentrations in a simulated use test, there were three reactors. A no-effect level for sensitization has not been determined although the lowest concentrations tested were in the product usage range.

Rastogi SC, Johansen JD, Menné T. Natural ingredients based cosmetics. Content of selected fragrance sensitizers. Contact Dermatitis. 1996 Jun;34(6):423-6. doi: 10.1111/j.1600-0536.1996.tb02246.x. 

Abstract. In the present study, we have investigated 42 cosmetic products based on natural ingredients for content of 11 fragrance substances: geraniol, hydroxycitronellal, eugenol, isoeugenol, cinnamic aldehyde, cinnamic alcohol, alpha-amylcinnamic aldehyde, citral, coumarin, dihydrocoumarin and alpha-hexylcinnamic aldehyde. The study revealed that the 91% (20/22) of the natural ingredients based perfumes contained 0.027%-7.706% of 1 to 7 of the target fragrances. Between 1 and 5 of the chemically defined synthetic constituents of fragrance mix were found in 82% (18/22) of the perfumes. 35% (7/20) of the other cosmetic products (shampoos, creams, tonics, etc) were found to contain 0.0003-0.0820% of 1 to 3 of the target fragrances. Relatively high concentrations of hydroxycitronellal, coumarin, cinnamic alcohol and alpha-amyl cinnamic aldehyde were found in some of the investigated products. The detection of hydroxycitronellal and alpha-hexylcinnamic aldehyde in some of the products demonstrates that artificial fragrances, i.e., compounds not yet regarded as natural substances, may be present in products claimed to be based on natural ingredients.

Andrade JC, Monteiro ÁB, Andrade HHN, Gonzaga TKSN, Silva PR, Alves DN, Castro RD, Maia MS, Scotti MT, Sousa DP, Almeida RN. Involvement of GABAA Receptors in the Anxiolytic-Like Effect of Hydroxycitronellal. Biomed Res Int. 2021 Jun 16;2021:9929805. doi: 10.1155/2021/9929805. PMID: 34222487; PMCID: PMC8225436.