Claim File c004 — Trolamine Salicylate

CAS 2174-16-5

Note: trolamine salicylate is a salicylate-class UVB filter, not a benzophenone. It is included in this collection for completeness as part of the older U.S. monograph filter set, and because it is one of the few water-soluble UVB chemical filters used historically in cosmetic and pain-relief products.

Section 1: Identity

• INCI / USAN: Trolamine Salicylate (also "Triethanolamine Salicylate", "TEA-Salicylate") [C1]
• IUPAC: 2,2′,2″-Nitrilotriethan-1-ol; 2-hydroxybenzoate (1:1 salt of triethanolamine and salicylic acid) [C1]
• Alternate forms: the cation/anion pair [HN(CH₂CH₂OH)₃]⁺ · [C₆H₄(OH)COO]⁻ [C1]
• CAS: 2174-16-5 [C1]
• Molecular formula: C13H21NO6 [C1]
• Molecular weight: 287.31 g/mol [C1]
• Physical: light-yellow to amber crystalline solid; sweet odor; mp ~57–59 °C; density ≈ 1.21 g/mL [C1]
• Solubility: water soluble (~68–73 g/L); soluble in lower alcohols; pH of 10% solution ~5.5–7.5 [C1]
• logKow: salicylate anion logD ≈ –1.5 (very polar/hydrophilic) [C2]

Regulatory status (current as of May 2026)

• Typical use levels (sunscreen, historical): 5–12% — required at high concentration because of weak absorptivity [C1]
• Typical use (analgesic): 10% in topical pain-relief creams [C1]

Section 2: UV Absorption Spectrum

• The chromophore is the salicylate (2-hydroxybenzoate) anion; triethanolamine is a non-absorbing counter-ion.
• λmax: ~298–302 nm in aqueous solution (the salicylate anion's longer-wavelength band); a smaller band near 235 nm is also present. In acidic protonated form λmax shifts slightly.
• Spectral coverage: ~260–315 nm — purely UVB; no useful absorption above ~315 nm (i.e. no UVA filtering capability whatsoever). [C1]
• Molar absorption coefficient: salicylate anion ε at ~298 nm ≈ 3.0–3.6 × 10³ M⁻¹·cm⁻¹ — roughly 5–7× weaker than BP-3 at its UVB peak. This is why high concentrations (≥8%) are required for SPF contribution. [C2 — standard UV-Vis tabulations of salicylate]
• E(1%, 1 cm) at 298 nm: ≈ 105–125 (computed from MW 287 and ε ≈ 3 × 10³) [C3]
• Solvent dependence: small. Salicylate is fully ionized in cosmetic-pH water systems; modest red-shift in the protonated form (low pH). The trolamine cation does not absorb in UV-A or UV-B.
• Functional classification: weak UVB filter. Useful only at very high % loadings. Provides minimal SPF contribution by itself; never used as a primary sunscreen active in modern products.

Section 3: Photodegradation

• Salicylates as a class are moderately photostable: the chromophore dissipates UV energy via excited-state intramolecular proton transfer (ESIPT) between the 2-OH and the carboxylate (analogous mechanism to that of methyl salicylate, used as a fluorescence standard for quantum-yield measurements). [C2]
• Photoproducts in aqueous direct photolysis: small amounts of salicylaldehyde, 2,3-dihydroxybenzoate, and 2,5-dihydroxybenzoate (gentisate) have been reported for salicylic acid; minor products only. [C2]
• Photodegradation kinetics: in dilute aqueous solution under simulated sunlight, k ≈ 10⁻⁶ s⁻¹ (i.e. half-life of many hours to days) — substantially more photostable than oxybenzone in absolute degradation rate, partly because absorbance is so low at solar wavelengths. [C2]
• Quantum yield: Φ_loss ≈ 10⁻⁴ in aqueous solution (low). [C2]
• Behavior in formulation: chemically stable in cream/gel/lotion vehicles. Volatility very low (salt). Compatible with most other actives.

Section 4: Notable issues

4.1 Salicylate toxicity (the dominant safety concern)

• Systemic salicylate exposure is the principal FDA concern. Topical salicylate-containing products have been associated with cases of salicylate poisoning when applied to large body-surface areas, especially in children. A landmark case (Arnold 2007) reported a fatality in a 17-year-old athlete attributable to chronic high-volume application of a methyl-salicylate / trolamine-salicylate analgesic cream. [C2]
• Chronic supratherapeutic exposure can produce tinnitus, GI bleeding, metabolic acidosis (high-dose salicylate toxidrome), particularly with concomitant heating pads or occlusive dressings.
• Coagulation effects: salicylates inhibit cyclo-oxygenase / platelet aggregation; cited by FDA as a concern for chronic high-area sunscreen use. Anticoagulant interactions (warfarin INR elevation) reported with topical salicylate creams. [C1 — FDA 2019/2021 orders]

4.2 Skin penetration

• Significant percutaneous absorption — 12–22% of applied dose absorbed in 12 h in some studies (Roberts et al. 1998 Br J Clin Pharmacol). This is substantially higher fraction-absorbed than most UV filters. The high penetration is the basis for both the analgesic effect and the systemic-toxicity concern.

4.3 Endocrine activity

• Not flagged as estrogenic. No notable endocrine-disruption signal in standard assays; not an ED concern in the way oxybenzone is.

4.4 Allergenicity

• Allergic contact dermatitis to triethanolamine (the cation) is well documented; allergy to the salicylate anion is rare. Cross-reactivity with other salicylates (methyl, glycol, octisalate, homosalate) is uncommon because the salicylate is the conserved part of all those molecules and the alkyl/ester portion typically determines sensitization potential. Triethanolamine itself is on most "common allergens" lists — patch-test prevalence ~0.5–2%. [C2]

4.5 Coral / aquatic toxicity

• Not a documented coral toxicant; not named in any sunscreen ingredient ban. Salicylates are biodegradable in WWTPs.

4.6 Effective SPF contribution

• At 12% in a typical o/w emulsion, trolamine salicylate alone delivers SPF ≈ 4–6 (rough order). It does not provide UVA protection. In modern sunscreen formulation, it is essentially obsolete as a primary UVB filter. Its current commercial relevance is overwhelmingly in topical analgesic (counter-irritant) products rather than sunscreens.

Confidence

• Identity / FDA monograph status → C1
• Absorption spectrum → C2 (well-known salicylate chromophore)
• Photodegradation → C2 (analogous to salicylic acid)
• FDA "not GRASE" proposed status → C1
• Skin absorption → C2

Key citations

1. FDA Proposed Rule, Federal Register 84 FR 6204 (26 Feb 2019), "Sunscreen Drug Products for Over-the-Counter Human Use".
2. FDA Proposed Order OTC000008 (24 Sept 2021), Amending OTC Monograph M020.
3. FDA Final Administrative Order OTC000006 (M020 final).
4. Roberts MS et al. Br J Clin Pharmacol 1998;46:355-363. doi:10.1046/j.1365-2125.1998.00792.x
5. Trolamine salicylate PubChem CID 25213.
6. CIR Final Report, Triethanolamine. Int J Toxicol 2013;32(3 Suppl):S46-S71.