Coumarin
Also known as Coumarin, 2H-1-Benzopyran-2-one, 1,2-Benzopyrone, Benzo-alpha-pyrone, 2H-Chromen-2-one, Tonka bean camphor
“EU SCCS says: restricted.”
Coumarin (CAS 91-64-5; 2H-1-benzopyran-2-one) is a naturally-occurring lactone found in tonka beans, sweet clover (Melilotus officinalis), woodruff, and many other plants. It is one of the original 26 EU mandatory-disclosure fragrance allergens (Annex III Reference 77) requiring label declaration when concentration exceeds 0.001% in leave-on or 0.01% in rinse-off cosmetic products. SCCS/1459/11 Table 13-1 (p. 104) classifies Coumarin as an established contact allergen in humans with rating +++ (101-1000 positive patch test reactions reported), categorised as Allergen of Special Concern. The clinical-vs-mechanistic picture is unusual: SCCS Table 8-1 LLNA data show pure coumarin has EC3 >50% (weak/non-sensitizer in mouse local lymph node assay), and Vocanson et al. 2006 (PMID 16685137) demonstrated pure coumarin does not exhibit irritant or sensitizing properties in animal testing or human subjects — concluding that observed allergic reactions are attributable to commercial-grade coumarin contaminants rather than the parent molecule. Despite this, real-world clinical sensitization is well-documented (Mutterer 1999 PMID 10208506 isolated coumarin as the responsible allergen in a fragrance-mix-negative patient; Ng 2025 PMID 40665691 reports recent ACD case to coumarin in a Melilotus-containing tinted moisturiser). Coumarin is NOT listed in the CIR Quick Reference Table — verified absent in both the December 2017/July 2018 and September 2022 QRT versions (alphabetical sequence Choline Chloride → Cichorium Intybus, no row in between) — consistent with the fragrance-allergen class pattern of CIR deferring to RIFM/IFRA/SCCS. SEPARATE FOOD-ADDITIVE CONTEXT: FDA prohibits Coumarin as a food additive under 21 CFR 189.130 (Federal Register order March 5, 1954, 19 FR 1239) on grounds of rodent hepatotoxicity (centrilobular necrosis); this is a FOOD ban only — not a cosmetic restriction — and human metabolism differs substantially from rodent (humans primarily produce 7-hydroxycoumarin of lower toxicity). At cosmetic disclosure thresholds (max 0.01%), dermal exposure is well below systemic-toxicity concern. Coumarin is the structural parent of the anticoagulant warfarin but coumarin itself has NO anticoagulant activity (a common misconception).
Provides characteristic sweet hay/vanilla/tonka fragrance note; widely used in perfumery and personal care for its warm, balsamic-vanillic profile
Naturally occurring in many plants (tonka beans, sweet clover, woodruff, lavender, sweetgrass) — a major fragrance constituent of botanical extracts used in fine fragrance and aromatherapy
Vocanson 2006 evidence that pure (high-purity) coumarin is non-sensitizing suggests achievable formulation strategy: tighter contaminant specifications could materially reduce real-world allergenicity
- · SCCS/1459/11 Table 13-1 rating +++ (101-1000 positive reactions): Allergen of Special Concern category; bold-typeset designation reserved for the more clinically significant fragrance sensitizers
- · Reg (EU) 2023/1545 expanded the allergen list to >80 substances; transition period for new products through July 2028
Regulated EU fragrance allergen (Annex III Reference 77): label declaration required above 0.001% (leave-on) or 0.01% (rinse-off); Coumarin is on the original 26-allergen list with extensively documented patch-test sensitization
Mechanistic ambiguity: pure coumarin shows weak/no sensitization in mouse LLNA (EC3 >50%) and Vocanson 2006 attributed observed allergenicity to commercial-grade contaminants, yet real-world clinical patch-test positivity remains common — formulators using high-purity coumarin may see different outcomes than those using technical-grade material
FDA prohibits Coumarin as a food additive under 21 CFR 189.130 (1954 Federal Register order) due to rodent hepatotoxicity (centrilobular hepatic necrosis); this is a FOOD ban only — not a cosmetic restriction — and human metabolism (primarily 7-hydroxycoumarin) is substantially less toxic than rodent (3,4-coumarin epoxide pathway). At cosmetic disclosure thresholds, dermal exposure remains well below systemic-toxicity concern
No CIR safety assessment exists: Coumarin absent from both the Dec 2017/Jul 2018 and Sept 2022 CIR QRT versions (verified by alphabetical traversal between 'Choline Chloride' and 'Cichorium Intybus') — toxicology coverage relies on SCCS, RIFM, and clinical literature rather than CIR
Common misconception: Coumarin is the structural parent of warfarin (anticoagulant drug), but coumarin itself has NO anticoagulant activity — only synthetic 4-hydroxycoumarin derivatives like warfarin and dicoumarol exhibit vitamin K antagonism
SCCS/1459/11 Opinion on Fragrance Allergens in Cosmetic Products (adopted 13-14 December 2011) — Table 13-1 lists Coumarin (CAS 91-64-5) …
“COUMARIN* 91-64-5 +++”— sccs_o_073.pdf, Table 13-1 'Established contact allergens in humans' (p. 104); category +++ defined p. 103 as 101-1000 positive test reactions reported; asterisk indicates Fragrance substances identified as allergens in the 1999 opinion of SCCNFP
EU Regulation 1223/2009 Annex III (Restricted Substances) — Reference 77: Coumarin / 2H-1-Benzopyran-2-one (CAS 91-64-5; EC 202-086-7); f…
“Reference 77, Coumarin / 2H-1-Benzopyran-2-one, CAS 91-64-5 (EC 202-086-7); the presence of this substance must be indicated in the list of ingredients when its concentration exceeds: 0,001 % in leave-on products; 0,01 % in rinse-off products”— EU Reg 1223/2009 Annex III, Reference 77 (Coumarin)