Diethylhexyl Syringylidenemalonate
Also known as DESM, Oxynex ST, Diethylhexyl Syringylidene Malonate, bis(2-ethylhexyl) 2-[(4-hydroxy-3,5-dimethoxyphenyl)methylidene]propanedioate
“No regulator has issued a verdict on this ingredient.”
Diethylhexyl Syringylidenemalonate (DESM, CAS 444811-29-4) is a synthetic photostabilizer with built-in antioxidant functionality, commercially available as Oxynex ST Liquid (Merck). The sole peer-reviewed study (PMID 16492073, Photochem Photobiol 2006) demonstrates that DESM stabilizes avobenzone via triplet-state energy transfer and reactive-species scavenging, enabling SPF >30 broad-spectrum formulations. DESM is listed in EU CosIng under the 'skin protecting' function category and is not registered in EU Annex VI as a primary UV filter. No CIR safety assessment exists for this ingredient and no independent toxicology or safety studies were identified in PubMed.
Photostabilizes avobenzone (UVA filter) by triplet-state energy transfer, improving photostability 7-8 fold at 5 MED exposure compared to unstabilized controls
Dual antioxidant-photostabilizer functionality from hindered phenolic (syringyl) moiety and benzylidenemalonate chromophore
Enables broad-spectrum SPF >30 formulations when combined with avobenzone and UVB filters (homosalate or octisalate)
Photostable itself under UV exposure; also quenches singlet oxygen and scavenges reactive species
EU CosIng lists function as 'skin protecting'; not classified as a primary UV filter requiring Annex VI listing
- · No independent safety or toxicology studies identified in PubMed; safety profile rests on formulator trade literature and a single sunscreen-design study
- · CIR has not assessed this ingredient (absent from the QRT as of 2018)
- · No EU SCCS opinion identified
- · Extremely low water solubility (~0.0001572 mg/L at 25°C); environmental fate and aquatic toxicity data unknown