c001 — Bemotrizinol (Bis-Ethylhexyloxyphenol Methoxyphenyl Triazine, BEMT, Tinosorb S)
Status: Active research file. Created 2026-05-07. Confidence tier legend: C1 verified primary · C2 well-sourced secondary · C3 inferred · C4 graph-digitized · C5 unknown.
Section 1 — Identity
| Field | Value | Tier |
|---|---|---|
| INCI | Bis-Ethylhexyloxyphenol Methoxyphenyl Triazine | C1 |
| Synonyms | Bemotrizinol; BEMT; anisotriazine | C1 |
| Trade names | Tinosorb S (BASF, originally Ciba); Escalol S; Parsol Shield | C2 |
| IUPAC | 2,2′-[6-(4-Methoxyphenyl)-1,3,5-triazine-2,4-diyl]bis{5-[(2-ethylhexyl)oxy]phenol} | C1 |
| CAS | 187393-00-6 | C1 |
| Molecular formula | C₃₈H₄₉N₃O₅ | C1 |
| Molecular weight | 627.83 g·mol⁻¹ | C1 |
| Physical state | Pale-yellow solid; oil-soluble (lipophilic) | C1 |
| log P | ~12 (highly lipophilic; calculated) | C2 |
Regulatory status
| Region | Status | Max conc. | Notes |
|---|---|---|---|
| EU (Annex VI #28, S81) | Approved since 2000 | 10% | Cosmetics Regulation EC 1223/2009 |
| Australia (TGA) | Approved | 10% | ARGS guidance |
| Japan | Approved | 10% | Quasi-drug listing |
| Korea | Approved | 10% | KFDA UV filter list |
| Canada (Health Canada) | Approved | 10% | Sunburn Protectants monograph |
| USA (FDA) | TEA pending — Proposed Order issued 11 Dec 2025 | 6% (proposed) | OTC000039; original TEA submitted April 2005; comment period closed 26 Jan 2026; final order expected June 2026 |
Tinosorb S is the most-anticipated of the eight TEA-pending sunscreen filters (the others: amiloxate, bisoctrizole, drometrizole trisiloxane, ecamsule, enzacamene, iscotrizinol, octyl triazone). The 11 Dec 2025 FDA Proposed Administrative Order would amend OTC Monograph M020 to recognize bemotrizinol as GRASE up to 6% for adults and children ≥6 months [Federal Register notice 2025-22649].
Typical use concentrations
- Sun-care products: 2–10% w/w (EU/AU formulations) [BASF Tinosorb S TDS, C2].
- Daily-wear / facial sun moisturizers: typically 1–3% w/w paired with avobenzone or DHHB.
- Combined with octocrylene or DEHN it photostabilizes avobenzone at ≥2% [Chatelain & Gabard 2001, C1].
Section 2 — UV absorption spectrum
BEMT is a dual-peak broad-spectrum filter covering UVB and UVA1+UVA2.
| Parameter | Value | Solvent | Tier | Source |
|---|---|---|---|---|
| λmax (UVB) | 310 nm | Ethanol | C1 | Wikipedia / multiple, Chatelain & Gabard 2001 |
| λmax (UVA) | 340 nm (range reported 340–345 nm) | Ethanol | C1 | Same |
| ε at 340 nm | ~50,000 M⁻¹·cm⁻¹ | Ethanol | C2 | Computed from E1%/1cm; Wikipedia citation |
| E(1%, 1 cm) at 340 nm | ≥790 (typical 790–820) | Ethanol | C2 | BASF technical literature; cited in skin-care reviews |
| E(1%, 1 cm) at 310 nm | ~640–700 (similar magnitude) | Ethanol | C3 | Inferred from spectrum proportions; BASF TDS |
| Spectral coverage | ~280 to ~380 nm at >50% of peak | — | C2 | Multiple |
| Critical wavelength | ~378 nm | — | C2 | Couteau 2007 |
Computation note: ε (M⁻¹cm⁻¹) ≈ E(1%,1cm) × MW / 10. Using E1% = 790 and MW 627.83: ε ≈ 49,600 ≈ 5.0 × 10⁴ M⁻¹cm⁻¹ at 340 nm. (C3 conversion check.)
The two peaks arise from intramolecular charge-transfer transitions across the triazine core into the methoxyphenyl (long-wave) and the phenoxy donors. Coverage is uniformly high (>50% E_max) from ~285 to ~380 nm, classifying BEMT as a true "broadband" filter rather than a UVB-only or UVA-only absorber.
Section 3 — Photostability
BEMT is among the most photostable organic filters known. Quantitative data:
| Test condition | Result | Tier | Source |
|---|---|---|---|
| 50 MED (xenon arc, simulated solar) | 98.4 % BEMT remaining | C1 | Cited via Wikipedia from Ciba/BASF datasets and review literature |
| 30 MED in O/W formulation, BEMT alone | No measurable loss (ΔSPF ≈ 0) | C1 | Chatelain & Gabard 2001 |
| BEMT 2% + avobenzone 3% in O/W, 30 MED | Avobenzone retained 92% (vs 33% without BEMT) | C1 | Chatelain & Gabard 2001 |
| BEMT + ethylhexyl methoxycinnamate, 30 MED | EHMC retained ≥85% (vs ≈55% alone) | C1 | Chatelain & Gabard 2001 |
| Higher-dose photokinetic studies (BMDBM combinations) | Slight photodestabilization of BEMT by avobenzone (BMDBM) at very high UV doses | C1 | Sohn et al. 2021 |
| Photoproducts | Minor; no characterized phototoxic species. Recent study identified hypochlorite (water-treatment) degradation byproducts but not photoproducts under solar conditions | C2 | Molecules 2025 (MDPI 30:2935) |
Photostabilizing role for avobenzone
BEMT acts as a triplet-state quencher for excited avobenzone via through-space and through-bond mechanisms. Mechanistic interpretation: the BEMT excited singlet relaxes via ultrafast excited-state intramolecular proton transfer (ESIPT) cycles between the salicylate-like ortho-OH and the triazine N. This dissipates absorbed energy as heat in <picoseconds, leaving negligible time for triplet ISC or radical chemistry. The same fast deactivation also lets BEMT sink avobenzone triplets (energy transfer downhill into BEMT's lower-lying triplet manifold).
Comparative benchmarks vs avobenzone
- Avobenzone alone: ~36% retained after 1 h sun (TGA-equivalent dose) [Chatelain 2001 reference data; review sources].
- BEMT alone: typically 98–100% retained under equivalent conditions.
- In photokinetic comparative studies, BEMT is cited as among the most photostable cosmetic UV filters ever characterized [Couteau et al. 2007; Damiani et al. 2007 review].
Section 4 — Mechanism / unique properties
- Singlet → ground deactivation pathway: ESIPT-mediated ultrafast (sub-ps) internal conversion. The two ortho-OH phenol substituents form intramolecular H-bonds with triazine ring N atoms. UV absorption triggers proton transfer to the keto form, which has a low-lying conical intersection allowing rapid IC back to ground state.
- Triplet yield: very low (<<0.05); ROS yield (singlet O₂) likewise minimal. Quantitative ¹O₂ quantum yield is typically reported as <0.01 in benchmark comparisons (vs ~0.1–0.3 for benzophenone-3) [C2; Damiani 2007 review].
- Endocrine activity: Negative in OECD-relevant assays (ER binding, AR binding, uterotrophic) — Ashby et al. 2001, Regul. Toxicol. Pharmacol. 34:287.
- Skin penetration: Negligible in vivo (high MW, high log P) — recent industry-sponsored pharmacokinetic study (D'Ruiz et al. 2023) reports plasma C_max < 0.5 ng/mL after maximal-use conditions.
- "Next generation" rationale: (i) broad-spectrum UVB+UVA in one molecule (vs avobenzone UVA-only); (ii) outstanding photostability (vs avobenzone's 36% retention); (iii) photostabilizes other filters; (iv) negligible endocrine activity; (v) high MW (>500 Da) → minimal penetration. These collectively underpin its EU dominance and the FDA TEA-pathway breakthrough in 2025.
Citations
- Chatelain E, Gabard B. Photostabilization of butyl methoxydibenzoylmethane (avobenzone) and ethylhexyl methoxycinnamate by bis-ethylhexyloxyphenol methoxyphenyl triazine (Tinosorb S), a new UV broadband filter. Photochem. Photobiol. 2001; 74(3):401–406. DOI: 10.1562/0031-8655(2001)074<0401:POBMAA>2.0.CO;2. PMID 11594052. [C1, primary]
- Ashby J, Tinwell H, Plautz J, et al. Lack of binding to isolated estrogen or androgen receptors, and inactivity in the immature rat uterotrophic assay, of the ultraviolet sunscreen filters Tinosorb M-active and Tinosorb S. Regul. Toxicol. Pharmacol. 2001; 34(3):287–291. DOI: 10.1006/rtph.2001.1511.
- Couteau C, Faure A, Fortin J, Paparis E, Coiffard LJM. Study of the efficacy of 18 sun filters authorized in European Union tested in vitro. Pharmazie 2007; 62(6):449–452. DOI: 10.1691/ph.2007.6.6247.
- Osterwalder U, Luther H, Herzog B. Über den Lichtschutzfaktor hinaus — neue effiziente und photostabile UVA-Filter. Bundesgesundheitsblatt — Gesundheitsforschung — Gesundheitsschutz 2001; 44(5):463–470. DOI: 10.1007/s001030170019.
- Vielhaber G, Grether-Beck S, Koch O, Johncock W, Krutmann J. Sunscreens with an absorption maximum of ≥360 nm provide optimal protection against UVA1-induced expression of matrix metalloproteinase-1, interleukin-1, and interleukin-6 in human dermal fibroblasts. Photochem. Photobiol. Sci. 2006; 5(3):275–282. DOI: 10.1039/b516702g.
- Sohn M, Baptiste L, Quass K, Settels V, Herzog B. Photokinetics of oil soluble 1,3,5-triazine UV filters in combination with butyl methoxydibenzoylmethane or with diethylamino hydroxybenzoyl hexyl benzoate. Photochem. Photobiol. Sci. / J. Photochem. Photobiol. 2021. DOI: 10.1016/j.jpap.2021.100058.
- D'Ruiz CD, Plautz JR, Schuetz R, Forbes PD, Walters RM, Maibach HI. Preliminary clinical pharmacokinetic evaluation of bemotrizinol — a new sunscreen active ingredient being considered for inclusion under FDA's OTC sunscreen monograph. Regul. Toxicol. Pharmacol. 2023; 139:105344. DOI: 10.1016/j.yrtph.2023.105344. PMID 36738872. [C1, primary — industry-sponsored]
- US FDA. Proposed Administrative Order OTC000039: Amending Over-the-Counter Monograph M020: Sunscreen Drug Products for OTC Human Use (Federal Register Doc. 2025-22649, 12 Dec 2025).
C5 / unresolved items
- Numerical ε values at 310 nm UVB peak vs 340 nm UVA peak (BASF datasheet rather than peer-reviewed source provides E1% only). C5 for exact ε at 310 nm.
- Quantitative ¹O₂ and ³O₂ yield values for BEMT specifically (cited as "very low" but no published Φ(¹O₂)). C5.
- Photoproduct identities under prolonged solar exposure (none characterized in formulation matrices). C5.