Hydroxycitronellal
The "lily-of-the-valley" note and a Fragrance Mix I allergen — a moderately common fragrance sensitiser found in floral soaps and perfumes
INCIHydroxycitronellal
- Category
- Fragrance
- Risk level
- medium
- Why it's flagged
- EU-labelled fragrance allergen and a Fragrance Mix I component
- Scent
- Lily-of-the-valley (muguet), green-floral, aldehydic — common in feminine perfumes and soaps
- Fragrance Mix I
- One of the 8 components of FM I, the primary fragrance-allergy patch-test screen
- Prevalence
- Roughly 1–3% positivity in fragrance-exposed/patch-tested groups; co-reacts with other FM I allergens
- EU labelling
- Must be named above 0.001% (leave-on) / 0.01% (rinse-off); on the expanded 2023 allergen list
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This ingredient may appear under any of these names:
Commonly found in
Possible reactions
- Allergic contact dermatitis at fragrance-contact sites
- Facial and neck rash
- Eyelid dermatitis from fragranced products
- Hand dermatitis from fragranced washes and cleaners
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What is hydroxycitronellal?
Hydroxycitronellal (INCI: Hydroxycitronellal; chemically 7-hydroxy-3,7-dimethyloctanal) is a synthetic fragrance aldehyde with a lily-of-the-valley (muguet), green-floral, aldehydic scent. It's a staple of floral perfume compositions — especially "fresh-floral" and feminine fragrances — and is very common in floral-scented soaps, body washes, lotions, and floral household products.
Its real significance is that it's one of the eight components of Fragrance Mix I (FM I), the internationally standardised patch-test mixture used to detect fragrance allergy — a place reserved for allergens of proven clinical importance.
Why it causes reactions
Hydroxycitronellal causes Type IV delayed hypersensitivity contact dermatitis. Its aldehyde group is reactive toward amino-acid residues in skin proteins (especially lysine), forming stable hapten–protein conjugates the immune system can recognise. Sensitisation rates run around 1–3% in fragrance-exposed/tested groups — moderately common — and co-sensitisation with other FM I members (like geraniol and cinnamyl alcohol) is frequent, so it rarely acts alone.
Because it's heavily used in soaps and washes, hand dermatitis and facial/neck reactions are typical; fragranced eye-area products can produce eyelid dermatitis.
If a patch test flags Fragrance Mix I, hydroxycitronellal is one of the eight suspects behind that single result. Individual-component testing is what turns "you're fragrance-allergic" into "this specific molecule is yours" — useful when you want to keep some scented products rather than avoid all of them.
How to spot and avoid it
- Read labels for Hydroxycitronellal (it's individually declared above threshold in the EU).
- Be cautious with floral-scented soaps and perfumes, its most common homes.
- Go fragrance-free for leave-on basics if you're FM I-positive, since these allergens co-occur.
- Ask for individual-component patch testing if you want to pin down which FM I allergen is yours.
Safer alternatives
- Fragrance-free personal care for face, neck, and hands.
- Lightly scented products built on non-allergenic aroma materials (verify the list).
- Fragrance-free household cleaners if hand dermatitis is the issue.
The bottom line
Hydroxycitronellal is the lily-of-the-valley note and a long-recognised Fragrance Mix I allergen — moderately common, frequent in floral soaps and perfumes, and often part of a multi-allergen fragrance sensitivity. Pin it down with FM I component testing, or simply go fragrance-free for the products that touch your skin most.
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References & further reading
- Fragrance Mix I and its components — overview DermNet
- Hydroxycitronellal contact allergy — review PubMed / Contact Dermatitis
- CosIng / Regulation (EU) 2023/1545 (labelled fragrance allergens) EUR-Lex