Diethylhexyl Syringylidenemalonate
Reviewed by Rosie · Last updated 18 Aug 2026
Also known as: Oxynex ST, Propanedioic acid, 2-[(4-hydroxy-3, 5-dimethoxyphenyl)methylene]-, 1, 3-bis(2-ethylhexyl) ester, [(4-hydroxy-3, Bis(2-ethylhexyl) ester, Bis(2-ethylhexyl) (4-hydroxy-3, 5-dimethoxybenzylidene)malonate, Bis(2-ethylhexyl) 2-[(4-hydroxy-3, 5-dimethoxyphenyl)methylidene]propanedioate
An ester that functions as an antioxidant and photostabiliser | Stabilises UV filters, especially avobenzone
Addresses
EWG Safety Score
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What Is Diethylhexyl Syringylidenemalonate?
Diethylhexyl syringylidenemalonate (DESM) is an ester that functions as an antioxidant and helps protect cosmetics from chemical or physical deterioration induced by light. This means it is a photostabilizer.
In this function, it also stabilizes many UV filters, most notably avobenzone. Research shows diethylhexyl syringylidenemalonate can increase critical wavelength in sunscreens (a measure of protection against UVA rays) and boost SPF in sunscreen formulas. At room temperature it is a viscous yellowish liquid or a low-melting solid.
Maximum usage levels for this antioxidant haven’t been established; however, amounts between 0.3–0.5% produce the desired photostabilizing effects in sunscreens.
Clinical Evidence & References
Published Research
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The New Sunscreens among Formulation Strategy, Stability Issues, Changing Norms, Safety and Efficacy Evaluations [https://www.mdpi.com/2079-9284/4/2/15]
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3-(3,4,5-Trimethoxybenzylidene)-2,4-pentanedione: Design of a novel photostabilizer with in vivo SPF boosting properties and its use in developing broad-spectrum sunscreen formulations [https://onlinelibrary.wiley.com/doi/abs/10.1111/ics.12344]
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Drug-excipient compatibility studies in binary mixtures of avobenzone [https://discovery.researcher.life/article/drug-excipient-compatibility-studies-in-binary-mixtures-of-avobenzone/7b63fcfbe2503f7b8aeeb48dbf371943]
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Design of a Photostabilizer Having Built-in Antioxidant Functionality and Its Utility in Obtaining Broad-Spectrum Sunscreen Formulations [https://onlinelibrary.wiley.com/doi/abs/10.1562/2005-07-15-RA-612]
From the Clinic
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Diethylamino Hydroxybenzoyl Hexyl Benzoate
Synthetic sunscreen agent that helps shield skin against UVA rays Approved as UV filter in many global markets but not in the U.S.
Diethylhexyl 2,6-Naphthalate
A photostabiliser and emollient used primarily in sun protection formulations
Diethylhexyl Butamido Triazone
Synthetic, oil-soluble UV filter
Disodium Phenyl Dibenzimidazole Tetrasulfonate
A water-soluble chemical UV filter used in modern sunscreen formulations
Drometrizole Trisiloxane
Known more commonly as Mexoryl XL Photostable UVA and UVB filter
Ecamsule
Photostable UVA filter Technical name is terephthalylidene dicamphor sulfonic acid
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