Drometrizole Trisiloxane (Mexoryl XL / DRT)

INCI: Drometrizole Trisiloxane IUPAC: 2-(benzotriazol-2-yl)-4-methyl-6-[2-methyl-3-[methyl-bis(trimethylsilyloxy)silyl]propyl]phenol PubChem CID: 9848888 · CAS: 155633-54-8 · DrugBank: DB11585 · MW: 501.8 g/mol · Formula: C₂₄H₃₉N₃O₃Si₃ · ChEMBL: not found gap/no-chembl-id

Drometrizole trisiloxane (trade name Mexoryl XL; abbreviated DRT or DT in the published literature) is an oil-soluble, photostable organic UV filter developed by L’Oréal R&D. It is a broad-spectrum UVA absorber covering both UVA-II (320–340 nm) and UVA-I (340–400 nm), with a peak absorption in the UVA-I range. Its defining structural feature is a benzotriazole chromophore (the photoreactive core) tethered to an organosilicone (trisiloxane) backbone — the silicon side-chain substantially enhances oil solubility and allows seamless incorporation into silicone-rich cosmetic emulsions without the requirement for solubilisers. DRT is L’Oréal-proprietary and is almost exclusively found in L’Oréal-family sunscreens (La Roche-Posay Anthelios, L’Oréal Paris, Vichy Capital Soleil). It is approved in the EU, UK, Australia, Canada, and several Asian markets but is not FDA-approved for US sunscreens — see § Regulatory status. For the broader photoprotection intervention context see uv-protection.

Mexoryl family note: L’Oréal markets two distinct compounds under the “Mexoryl” name that are frequently co-formulated:

Mexoryl SX (ecamsule, terephthalylidene dicamphor sulfonic acid) → water-soluble, UVA-II specialist (~λmax 345 nm). See ecamsule.
Mexoryl XL (drometrizole trisiloxane, this page) → oil-soluble, broader UVA coverage spanning UVA-II + UVA-I.

The two filters are functionally complementary: Mexoryl SX anchors UVA-II protection; Mexoryl XL extends coverage through UVA-I. Their co-formulation in Anthelios products is intentional and represents one of the most extensively clinically-tested sunscreen stacks for lupus photodermatosis and general photoaging ¹ ².

Cross-family note: Mexoryl XL is structurally a benzotriazole-derived filter, sharing chromophore ancestry with bemotrizinol (BEMT/Tinosorb S — a bis-ethylhexyloxyphenol methoxyphenyl triazine) and bisoctrizole (MBBT/Tinosorb M). However, DRT’s organosilicone tail is unique to this compound class; it should not be confused with the 1,3,5-triazine ring system of tinosorb-a2b, iscotrizinol, or the newer mexoryl-400 (MCE) which is a cyclohexenylidene-cyanoacetate (not a benzotriazole). For the emerging ultra-long UVA-I gap-filling filters (380–400 nm), see mexoryl-400 (MCE, λmax 385 nm) and triasorb (PBT, 400–450 nm HEV extension).

Why UVA-II + UVA-I coverage matters

Ground-level solar UV arriving at skin is dominated by UVA (~95%) across the 320–400 nm window. The UVA range drives:

Reactive oxygen species (ROS) production — indirect DNA damage (8-OHdG, single-strand breaks), lipid peroxidation, mitochondrial dysfunction in dermal fibroblasts
Matrix metalloproteinase induction (MMP-1/MMP-3/MMP-9) via AP-1/NF-κB, degrading dermal collagen-I and elastin — the proximal molecular mechanism of photoaging ³
Persistent pigment darkening (PPD) and immediate pigment darkening (IPD) — the basis of UVA protection rating systems
Photoimmunosuppression — Langerhans cell loss, impaired contact-hypersensitivity responses
Photoaggravation of skin diseases — lupus erythematosus, polymorphous light eruption, and related photodermatoses are predominantly UVA-triggered

DRT provides high molar absorptivity across both UVA-II (320–340 nm) and UVA-I (340–400 nm), making it one of the broadest-coverage single organic UV filters in the cosmetic arsenal as of 2026. This breadth, combined with its photostability, distinguishes it from avobenzone (UVA-I specialist but photounstable) and Mexoryl SX (UVA-II specialist). However, DRT’s absorption is concentrated in the classical UVA range (320–400 nm) and does not extend into the ultra-long UVA-I / visible blue region (380–450 nm) covered by mexoryl-400 (λmax 385 nm) and triasorb (400–450 nm HEV). gap/comparative-spectral-data-needed for precise ε values at key sub-wavelengths.

Mechanism

DRT is a hydroxyphenyl benzotriazole — the phenolic hydroxyl group and benzotriazole ring form an intramolecular hydrogen bond that creates an excited-state intramolecular proton-transfer (ESIPT) pathway. On absorbing a UV photon:

The chromophore is raised to its excited singlet state (S₁)
ESIPT transfers a proton from the phenol to the triazole nitrogen, producing a tautomeric excited state
The excited tautomer undergoes rapid non-radiative relaxation (internal conversion + vibrational energy dissipation → heat) back to the ground state keto-form
Proton transfer reversal regenerates the enol ground-state tautomer

This ESIPT mechanism allows highly efficient photon absorption and energy dissipation without generating photoreactive triplet states or singlet oxygen to any significant extent — in contrast to UV absorbers that produce ROS as photoproducts. The result is high photostability: DRT does not undergo significant photodegradation under UV irradiation, and critically, it does not sensitise degradation of co-formulated avobenzone (a major problem with octinoxate + avobenzone combinations) ⁴.

The trisiloxane appendage is purely a solubility/formulation modification — it does not participate in the photochemical mechanism. It renders DRT:

Highly oil-soluble — compatible with silicone-rich formulations
Poorly water-soluble — minimal leaching in water/sweat
High molecular weight (501.8 Da) — reduced dermal penetration probability vs. low-MW organic filters

Regulatory status

Region	Status	Max concentration
EU (EMA/EC)	Annex VI entry (EU Cosmetics Regulation 1223/2009); authorized as UV filter. SCCS evaluated DRT as part of early safety review.	≤15% in finished product per Annex VI
United Kingdom (MHRA)	Recognized post-Brexit as authorized cosmetic UV filter (retained EU Annex VI list).	≤15%
Australia (TGA)	Listed as permitted UV filter in listed sunscreen goods; usable at ≤10% per TGA compositional guidelines.	≤10%
Canada (Health Canada)	Approved as cosmetic UV filter.	per approved conditions
United States (FDA)	Not GRASE. Not listed in 21 CFR §352 OTC sunscreen monograph. No Time and Extent Application (TEA) filed or pending publicly for DRT. US-market L’Oréal / LRP / Vichy / CeraVe formulations cannot contain DRT.	—
Japan / South Korea / Asia	Approved in multiple markets per L’Oréal regional regulatory filings.	varies by market

The FDA exclusion reflects the US OTC monograph backlog — the same regulatory “GRASE gap” that affects bemotrizinol, bisoctrizole, and mexoryl-400. This is a regulatory-inertia gap, not a safety finding. The Diffey 2016 editorial in JAMA Dermatology ⁵ and the Turner 2025 review in Photodermatol Photoimmunol Photomed ⁶ both specifically cite DRT as among the EU-approved filters that would improve US photoprotection options if approved. The US DSSA (Sunscreen Innovation Act, 2014) and subsequent CARES Act provisions were intended to accelerate this process, but as of June 2026 no additional chemical UV filters have received FDA GRASE status.

Clinical-stage assignment: approved-ex-us per R52 convention — EU/UK/AU/CA real-world marketing authorization exists; US is the gap jurisdiction.

Human evidence

The evidence base for DRT specifically (as opposed to DRT-containing formulations) is thin. Most published clinical data uses Anthelios-class formulations containing DRT alongside ecamsule (Mexoryl SX), avobenzone, octocrylene, and/or mineral filters — making DRT-specific effect attribution impossible. No single-agent DRT vs. placebo clinical trial has been published.

Lupus photodermatosis (highest-quality evidence)

Study	Design	n	Key result
Stege 2000 ¹	Double-blind, intra-individual comparative, photoprovocation test	11 LE patients	Anthelios formula containing Mexoryl XL + Mexoryl SX + Parsol 1789 + octocrylene + TiO₂ was “by far the most effective” of tested sunscreens, preventing UV-induced lupus lesions in all 11 patients; inferior formulations without this filter stack failed to protect
Carrera 2008 ⁷	In vivo human, melanocytic nevi photoprotection model	4 patients	DRT-containing Anthelios formulation “appeared to avoid” UVR-induced melanocytic activation and keratinocyte proliferation vs unprotected areas; no comparator without DRT

The Stege 2000 trial is the most-cited clinical validation of the Mexoryl SX + XL combination. Its finding is not specific to DRT — the benefit could reflect the co-formulation — but no other broad-spectrum filter combination of that era demonstrated comparable photoprotection in LE.

Pigmentation prevention

Study	Design	n	Key result
Moyal 2004 ²	Comparative, standardized pigmentation-provocation model	Not specified	UVA protection correlating with Mexoryl SX concentration; DRT-containing formulas showed better pigmentation prevention; “high UVA protection essential to prevent pigmentation”

Evidence gaps

No published RCT or cohort study specifically testing DRT addition/removal within an otherwise identical formula.
No human biopsy data (CPD, 6-4PP, 8-OHdG) specifically attributable to DRT contribution.
No long-term photoaging RCT with DRT-containing vs DRT-absent matched sunscreens (cf. Hughes 2013 standard in the photoprotection literature — the landmark RCT showing 24% less skin aging with daily vs discretionary sunscreen).
All mechanistic evidence for DRT’s specific UVA coverage role is spectroscopic, not biological.

gap/no-independent-replication · gap/no-drt-isolated-efficacy-data · gap/no-biopsy-endpoint

Safety

Established safety profile

DRT has been in commercial use since ~2001 (original Anthelios launch) and is present in L’Oréal’s most widely-used global sunscreen lines.
Photostability: High — DRT does not degrade significantly on UV exposure, unlike avobenzone. No photosensitizer activity detected in standard phototoxicity assays.
Dermal penetration: Low, based on compound physicochemistry (MW 501.8 Da; high log P due to trisiloxane; primarily partitions into stratum corneum lipid bilayers). No pharmacokinetic studies equivalent to the FDA Matta 2019/2020 JAMA maximal-use protocols have been published for DRT — this is an evidence gap gap/no-fda-pk-study, though it reflects FDA jurisdiction, not a safety finding.
No reproductive/endocrine-disruption concerns identified in the reviewed literature. DRT lacks structural features associated with benzophenone-type estrogenicity (no carbonyl groups in the right geometry). The 2025 comprehensive endocrine review ⁸ covers UV filters broadly; DRT-specific endocrine data are absent from the published literature.

Allergic contact sensitization

Two case reports document allergic contact dermatitis (ACD) to DRT:

Report	Design	Finding
Hughes 2005 ⁹	Case report, n=1 + patch-test panel	ACD to DRT in a sunscreen; concomitant sensitivities to multiple UV filters; patch test confirmed DRT as primary sensitizer
Pastor-Nieto 2023 ¹⁰	Case report, n=1	ACD to DRT in a woman subsequently diagnosed with frontal fibrosing alopecia (FFA); the co-diagnosis is notable — FFA is epidemiologically associated with sunscreen use, though causal mechanism is debated

Both are case reports — they document that DRT sensitization is possible, but provide no population-level incidence data. The FFA association noted in Pastor-Nieto 2023 is an ongoing area of investigation; no causal mechanism from DRT specifically to FFA has been established.

Environmental persistence

Fagervold et al. 2025 (PMID 40782226) ¹¹ found DRT showed no biodegradation by marine sediment microorganisms after 100 days of incubation — consistent with findings for most modern organic UV filters (triazine-class and benzotriazole-class). Wu et al. 2025 (PMID 40784479) detected DRT in coastal waters of the East China Marginal Seas at levels up to 0.31 ng/L, with marine organism exposure risk characterized as low to medium. Environmental persistence is not a human-health safety concern but is relevant to ecological risk framing. gap/long-term-unknown (aquatic endpoints)

Formulation context and product availability

DRT is an L’Oréal-proprietary ingredient. Its global commercial use is almost entirely within the L’Oréal family of brands:

Brand line	Products	Regions where DRT is present
La Roche-Posay Anthelios (SPF 50+ EU formulas)	Fluid SPF 50+, Melt-in Cream, Pocket SPF 50+	EU / UK / CA / AU / Asia
La Roche-Posay Anthelios (US formulas)	Melt-In Milk SPF 60/100, Clear Skin SPF 60, etc.	No DRT — US formulas use avobenzone/homosalate/octisalate/octocrylene
L’Oréal Paris Revitalift (EU)	Revitalift SPF 50 day cream	EU / UK
Vichy Capital Soleil (EU)	Multiple SPF 50+ SKUs	EU / UK
CeraVe AM Moisturizer (EU formulation)	EU SPF 50 AM moisturizer	EU (not US)
Garnier (select EU SPF formulas)	Some SPF-enriched moisturizers	EU

The characteristic pattern: any L’Oréal-family SPF 50+ EU sunscreen with “Mexoryl SX + Mexoryl XL” in the ingredient list contains DRT. US formulations of the same products are reformulated without DRT.

DRT in context: Mexoryl pairing and the UVA stack

In most L’Oréal formulations, DRT (Mexoryl XL) is co-formulated with ecamsule (Mexoryl SX). The combination provides:

Contribution	Mexoryl SX (ecamsule)	Mexoryl XL (DRT)
Primary absorption range	UVA-II (315–345 nm, λmax ~345)	UVA-II + UVA-I (310–380 nm, broader)
Solubility	Water-soluble	Oil-soluble
Photostability	Photostable	Photostable
Critical wavelength contribution	Extends CW	Extends CW further
FDA status	Approved (GRASE) — ecamsule received GRASE designation via the Abbreviated New Drug Application pathway in 2006	Not approved

Note: ecamsule (Mexoryl SX) is the only new-generation EU UV filter to have received FDA approval, via a specific manufacturer-sponsored NDA pathway in 2006 (Anthelios SX — La Roche-Posay NDA021502; L’Oréal also holds NDA021501 for Capital Soleil and NDA021471/NDA022009 for other Anthelios products containing ecamsule). DRT did not receive a similar filing. This means that US-market Anthelios products can include ecamsule but not DRT.

For users purchasing EU/UK/CA formulations, the DRT + ecamsule pairing provides more comprehensive UVA-II + UVA-I coverage than any currently available US-GRASE filter stack. For ultra-long UVA-I (380–400 nm) coverage, the Anthelios UVMune 400 line additionally incorporates mexoryl-400 (MCE); that represents a distinct third L’Oréal filter active, not a DRT sub-variant.

R16 intervention matrix

Hallmarks linked: genomic-instability (UV-induced CPD/6-4PP/8-OHdG burden); loss-of-proteostasis (MMP-driven collagen/elastin fragmentation); chronic-inflammation (UV → NF-κB cytokine induction)
Matrix row: DRT appears in the [[genomic-instability]], [[loss-of-proteostasis]], and [[chronic-inflammation]] Dataview blocks via hallmarks: frontmatter. No new mechanism class added to intervention-classes.md — UV-filter-absorption is an existing sub-value used on sibling pages mexoryl-400 and triasorb; UVA-broadband-coverage describes the DRT-specific spectral breadth and is consistent with the UV-filter class definition.
Translation gap: human-evidence-strong — the underlying UV-prevention → photoaging-reduction causal chain is well-established (Hughes 2013; Fisher 1996); the gap is DRT-specific attribution, not the photoprotection paradigm itself.

Cross-references

uv-protection — umbrella photoprotection intervention page
mexoryl-400 — sibling Mexoryl-family filter (MCE, ultra-long UVA-I / 380–400 nm, L’Oréal)
ecamsule — Mexoryl SX, the complementary water-soluble UVA-II filter always co-formulated with DRT in Anthelios products
triasorb — TriAsorB / PBT, competing 380+ nm + HEV filter (Pierre Fabre / Avène)
bemotrizinol — BEMT / Tinosorb S, another broad-spectrum EU UV filter
bisoctrizole — MBBT / Tinosorb M, another broad-spectrum EU UV filter
iscotrizinol — UV-A / UV-B filter, s-triazine class
tinosorb-a2b — UV filter, ancillary reference
genomic-instability — UV-induced DNA photoproducts
loss-of-proteostasis — MMP-driven ECM degradation
chronic-inflammation — UV-NF-κB-cytokine axis
skin-aging — primary photoaging clinical phenotype
fisher-1996-photoaging-ap1-mmp — mechanistic anchor (AP-1/NF-κB/MMP cascade)

Footnotes

doi:10.1034/j.1600-0781.2000.160604.x · Stege H, Budde A, Grether-Beck S, Krutmann J · Photodermatol Photoimmunol Photomed 2000;16(6):256–259 · double-blind intra-individual comparative · n=11 LE patients · photoprovocation test; sunscreen A (Mexoryl SX + XL + Parsol 1789 + octocrylene + TiO₂) “by far the most effective” at preventing UV-induced lupus lesions; all 11 patients protected · DRT contribution not isolated from co-filters · gap/no-fulltext-access ↩ ↩²
doi:10.1111/j.1600-0781.2004.00111.x · Moyal D · Photodermatol Photoimmunol Photomed 2004;20(5):243–247 · comparative pigmentation-provocation model · n not specified · high UVA protection (with Mexoryl SX + XL) essential to prevent UV-induced pigmentation; protection correlates with UVA absorber concentration · DRT role inferred from spectral coverage, not isolated · gap/no-fulltext-access ↩ ↩²
doi:10.1038/379335a0 · Fisher GJ, Datta SC, Talwar HS, et al. · Nature 1996;379(6563):335–339 · in vivo human (buttock skin) · n=15 · sub-erythemogenic UV (0.01 MED) activates AP-1 and NF-κB within minutes → MMP-1/3/9 transcription → collagen/elastin degradation → mechanistic anchor for photoaging (UV-band-agnostic at dose level) ↩
doi:10.1111/j.1468-3083.2007.02580.x · Antoniou C, Kosmadaki MG, Stratigos AJ, Katsambas AD · J Eur Acad Dermatol Venereol 2008;22(9):1110–1119 · review · DRT photostability noted alongside comparison of filter classes; no original trial data ↩
doi:10.1001/jamadermatol.2015.5360 · Diffey B · JAMA Dermatol 2016;152(4):380–381 · editorial · discusses regulatory gap between EU and US for newer UV filters including DRT; precautionary-principle framing of FDA non-approval ↩
doi:10.1111/phpp.70032 · Turner CW, Torgerson L · Photodermatol Photoimmunol Photomed 2025;41(5) · review · explicitly identifies DRT among EU-approved advanced UV filters unavailable in US due to regulatory inertia; argues modernized FDA process needed to reduce UV-induced cancer burden · hybrid OA ↩
doi:10.1159/000120477 · Carrera C, et al. · Dermatology 2008;216(4):299–307 · in vivo human photoprotection model (melanocytic nevi) · n=4 patients · DRT-containing Anthelios formula appeared to prevent UVR-induced nevus melanocytic activation and keratinocyte proliferation vs unprotected halves; small n; no DRT-isolated comparator arm · Note: this DOI resolves to a 1989 pediatric neurosurgery paper (Kaneko et al.) — the Carrera 2008 Dermatology citation details are unverifiable via CrossRef; DOI may be incorrect · gap/unverifiable-doi gap/no-fulltext-access ↩
doi:10.1007/s40572-025-00492-9 · Jaskulak M, Cinkusz M, Franchuk K, Zorena K · Curr Environ Health Rep 2025 · comprehensive review 2014–2024 · covers UV filter endocrine/reproductive health concerns broadly; DRT-specific endocrine data absent from published literature ↩
doi:10.1111/j.0105-1873.2005.0566a.x · Hughes TM, et al. · Contact Dermatitis 2005;52(4):226–227 · case report · n=1 + patch-test panel · allergic contact dermatitis to DRT in sunscreen; concomitant sensitivities to other UV filters; first published DRT sensitization case ↩
doi:10.1111/cod.14370 · Pastor-Nieto MA, Gatica-Ortega ME · Contact Dermatitis 2023;89(3):215–217 · case report · n=1 · ACD to DRT in a woman subsequently diagnosed with frontal fibrosing alopecia; co-diagnosis is notable but causality not established · hybrid OA ↩
doi:10.1007/s11356-025-36772-y · Fagervold SK, et al. · Environ Sci Pollut Res Int 2025;32(33):19823–19835 · marine sediment microcosms · DRT showed no biodegradation after 100 d; most modern organic filters similarly persistent; environmental-persistence concern · parallel finding to TriAsorB (Fagervold 2025 = same paper; this study also tested DRT specifically) ↩

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drometrizole-trisiloxane