1 Raw Material Properties and Sunscreen Positioning of Octocrylene

1.1 Basic Information

The Scientific Committee on Consumer Safety (SCCS) describes octocrylene as a yellow, transparent, viscous liquid with a relative molecular mass of approximately 361.5, low water solubility, and a high octanol–water partition coefficient.[1]

It should be noted that benzophenone may be present as an impurity and as a storage-related degradation product of octocrylene. The SCCS and current European Union regulations require it to be monitored and maintained at trace levels. Relevant storage studies may be used to investigate changes in benzophenone content as a function of time, temperature, and product composition.[1][8][11]

1.2 Which Wavelength Region Does Octocrylene Primarily Protect Against?

The absorption maximum of octocrylene is approximately 303 nm. It primarily absorbs UVB and extends into part of the short-wavelength UVA region. Its absorption intensity decreases substantially at longer UVA wavelengths, and it therefore cannot independently provide a complete broad-spectrum sunscreen system.

UVB primarily affects the epidermis. After deoxyribonucleic acid (DNA) absorbs UVB radiation, adjacent pyrimidine bases may form cyclobutane pyrimidine dimers and 6-4 photoproducts. If these lesions are not accurately repaired, genetic mutations may occur.

UVA penetrates more deeply into the skin and can excite endogenous chromophores, generating various reactive oxygen species (ROS) that contribute to membrane lipid oxidation, mitochondrial damage, collagen degradation, and oxidative DNA damage.[2]

The principal contributions of octocrylene in sunscreen systems include:

① absorbing UVB and reducing the ultraviolet burden associated with erythema and sunburn;

② absorbing a small proportion of short-wavelength UVA and supplementing protection in this wavelength region;

③ contributing to a broad-spectrum absorption system when combined with filters specifically covering long-wavelength UVA;

④ improving the solubility and formulation stability of certain oil-soluble UV filters.

The sun protection factor (SPF) is primarily calculated on the basis of the ability of ultraviolet radiation to induce erythema. Because the erythema action spectrum is particularly sensitive to UVB, octocrylene can make a substantial contribution to SPF. However, SPF alone does not fully represent protection against long-wavelength UVA.

2.1 Molecular Structure

The condensed structural formula of octocrylene may be represented as:

(C₆H₅)₂C=C(CN)C(=O)OCH₂CH(C₂H₅)CH₂CH₂CH₂CH₃

The molecule can be divided into two principal functional regions:

Diphenyl cyanoacrylate chromophoric region │ 2-Ethylhexyl hydrophobic region

(C₆H₅)₂C=C(CN)C(=O)O — CH₂CH(C₂H₅)CH₂CH₂CH₂CH₃

The chromophoric region is responsible for ultraviolet absorption, whereas the 2-ethylhexyl region mainly influences lipophilicity, the liquid state, and formulation compatibility.

2.2 Why the Chromophoric System Can Absorb Ultraviolet Radiation

The energy and wavelength of a photon satisfy the following relationship:

E = hc/λ

where:

• E represents photon energy;

• h represents Planck’s constant;

• c represents the speed of light;

• λ represents the wavelength of light.

The shorter the wavelength, the higher the energy of an individual photon.

The aromatic rings, carbon–carbon double bond, cyano group, and ester carbonyl group in octocrylene collectively form a chromophoric system capable of electron delocalization. When the energy of an ultraviolet photon matches the energy difference between the molecular ground state and an excited state, a π electron can be promoted from an occupied orbital to a higher-energy antibonding orbital. Its ultraviolet absorption may therefore be primarily attributed to a π→π* transition.

The structural units have different functions:

① the aromatic rings provide π-electron systems and extend the range of electron delocalization;

② the carbon–carbon double bond connects the cyanoacrylate core with the diphenyl-substituted structure;

③ the cyano group exerts a strong electron-withdrawing effect and can alter the electron density around the double bond;

④ the ester carbonyl group contributes to regulation of the molecular energy levels and charge distribution.

Because of steric hindrance, the two phenyl rings may not always remain completely coplanar with the central double bond. The actual degree of conjugation in octocrylene is therefore also affected by molecular conformation, solvent polarity, and the surrounding molecular environment. Its absorption maximum and molar absorptivity may vary slightly among different formulations.

The fact that octocrylene primarily absorbs UVB rather than long-wavelength UVA indicates that the energy required for its principal electronic transition remains relatively high. Long-wavelength UVA filters such as avobenzone possess different electronic structures and lower effective excitation energies, enabling them to absorb ultraviolet radiation at longer wavelengths.

2.3 Why the 2-Ethylhexyl Structure Provides Lipophilicity

The 2-ethylhexyl moiety is composed mainly of nonpolar hydrocarbon structures and cannot form sufficiently favorable hydrogen-bonding interactions with water. Octocrylene therefore has very low water solubility and preferentially partitions into oils, esters, and other hydrophobic components.

The branched structure also hinders regular molecular packing, making it difficult to form a compact and stable crystal lattice. This is one of the principal reasons why octocrylene is a viscous liquid at room temperature.

Its liquid and lipophilic characteristics provide the following formulation functions:

① mixing with esters, hydrocarbons, and other oil-phase ingredients;

② dissolving or assisting the dispersion of certain solid organic UV filters;

③ improving the spreadability of sunscreen products during application;

④ increasing the solubility margin of solid UV filters and reducing the likelihood of crystallization after drying;

⑤ promoting the retention of octocrylene in the hydrophobic regions of the sunscreen film.

These are formulation functions associated with dissolution, partitioning, and rheology and are not equivalent to polymeric film formation.

3 Photochemical Cycle of Octocrylene Following Ultraviolet Absorption

3.1 Ultraviolet Photons First Excite Electrons

Under normal conditions, octocrylene is in its electronic ground state, which can be represented as OCR(S₀). OCR denotes octocrylene, and S₀ denotes the ground singlet state.

After absorbing an ultraviolet photon, an electron enters a higher excited singlet state:

OCR(S₀) + hν → OCR(Sₙ)

where:

• hν represents the energy of the absorbed photon;

• Sₙ represents a higher-energy excited singlet state.

The molecule generally undergoes vibrational relaxation and internal conversion within an extremely short period, descending from the higher excited state to the lower excited singlet state S₁:

OCR(Sₙ) → OCR(S₁)

3.2 Ideal Pathway of Nonradiative Deactivation and Heat Dissipation

The ideal cycle through which octocrylene performs its sunscreen function can be represented as follows:

OCR(S₀) + hν

↓ Ultraviolet absorption

OCR(Sₙ)

↓ Vibrational relaxation and internal conversion

OCR(S₁)

↓ Nonradiative deactivation

OCR(S₀) + heat

When the electron returns from the excited state to the ground state, the excitation energy can be converted into stretching, bending, and torsional motions of chemical bonds. The molecule, now in a state of elevated vibrational energy, subsequently collides with surrounding oils, water, polymers, and other UV filters, dispersing the energy among the vibrational, rotational, and translational motions of many molecules.

Macroscopically, this energy appears as a very small quantity of heat. Because the energy is distributed among a large number of molecules and over a relatively large application area, it generally does not produce a perceptible local increase in temperature.

Ultraviolet energy does not remain stored in octocrylene molecules for prolonged periods. After an organic UV filter absorbs a photon, the excitation energy is generally dissipated within a short period through vibrational relaxation, internal conversion, and other deactivation pathways. The exact timescale and relative contribution of each pathway depend on the molecular structure and surrounding medium, while a small proportion of excited states may enter longer-lived or chemically reactive pathways.[3]

3.3 Photostability Depends on Competition Among Multiple Pathways

Excited octocrylene molecules do not all return to the ground state through the same pathway. The principal competing processes include:

① Nonradiative deactivation: the molecule recovers its original structure, and the energy is converted into heat;

② Conformational change or isomerization: the molecular geometry changes, and the absorption characteristics may change temporarily or persistently;

③ Intersystem crossing: an excited singlet state is converted into an excited triplet state;

④ Energy or electron transfer involving oxygen: singlet oxygen or other reactive oxygen species may be formed;

⑤ Irreversible photodegradation: bond cleavage, rearrangement, or formation of new chemical products occurs.

Intersystem crossing can be represented in simplified form as:

OCR(S₁) → OCR(T₁)

T₁ denotes the lowest excited triplet state. Return from the triplet state to the ground state is restricted by electron-spin selection rules. The triplet state therefore generally has a longer lifetime than an excited singlet state and consequently has a greater opportunity to react with oxygen or other molecules.

One theoretically possible competing process can be illustrated as follows:

OCR(T₁) + ³O₂ → OCR(S₀) + ¹O₂

Here, ³O₂ denotes ground-state triplet oxygen, and ¹O₂ denotes singlet oxygen. This reaction represents a possible energy-transfer pathway and does not indicate that it is the principal energy-dissipation route for octocrylene in all formulations.

The photostability of octocrylene depends on the following factors:

① the rate at which the molecule returns to the ground state;

② the proportion and lifetime of triplet-state formation;

③ the oxygen concentration in the formulation;

④ solvent polarity and viscosity;

⑤ the presence of other UV filters, antioxidants, and metal ions;

⑥ the wavelength, intensity, and duration of irradiation.

Photostability does not mean that no chemical change occurs. Rather, it means that, under specified irradiation conditions, non-destructive deactivation accounts for a sufficiently high proportion of the processes and the UV filter retains adequate ultraviolet absorption capacity.[3]

4 How Octocrylene Improves the Stability of Avobenzone Systems

4.1 Why Avobenzone Is Susceptible to Photodegradation

Avobenzone is a long-wavelength UVA filter with an absorption maximum generally located at approximately 357–360 nm. It contains a β-diketone structure and exists in a tautomeric equilibrium between keto and enol forms.

The chelated enol form has strong long-wavelength UVA absorption. After absorbing UVA, avobenzone may undergo:

① molecular conformational changes;

② keto–enol tautomerization;

③ intersystem crossing and formation of a triplet state;

④ reactions with oxygen or other formulation components;

⑤ bond cleavage, free-radical reactions, and irreversible photodegradation.

When the proportion of the effective enol form decreases, or when the molecule forms degradation products with weaker absorption capacity, the UVA absorption of the product decreases during irradiation. The actual photostability of avobenzone is also affected by the solvent, oxygen, concentration, and other UV filters.[3]

4.2 Three Types of Synergistic Effects That May Involve Octocrylene

4.2.1 Sharing the Short-Wavelength Photon Load

Octocrylene absorbs UVB and a small portion of short-wavelength UVA and can absorb part of the photon load in the region where its absorption spectrum overlaps with that of avobenzone. Octocrylene has weak absorption in the long-wavelength UVA region and therefore cannot replace avobenzone or resolve all avobenzone photodegradation problems through spectral screening alone.

4.2.2 Participation in Excited-State Quenching

Excited-state quenching refers to the shortening of the lifetime of an excited molecule through collisions, energy transfer, electron transfer, or related processes.

A general triplet–triplet energy-transfer process can be represented as:

D(T₁) + A(S₀) → D(S₀) + A(T₁)

where:

• D represents the excitation-energy donor;

• A represents the energy acceptor;

• T₁ represents an excited triplet state;

• S₀ represents the electronic ground state.

If the acceptor can rapidly return to the ground state through a nonradiative process after receiving the energy, the probability that the donor triplet state will participate in free-radical reactions or photodegradation may be reduced.

This process generally requires the following conditions:

① the triplet-state energy levels of the donor and acceptor must permit energy transfer;

② the two molecules must come into sufficiently close contact;

③ the energy-transfer rate must be able to compete with the photodegradation rate of the donor;

④ after receiving the energy, the acceptor must be able to deactivate through a comparatively non-destructive pathway.

Octocrylene is commonly used to improve the photostability of avobenzone-containing systems. However, the mere presence of both ingredients does not confirm the occurrence of highly efficient direct triplet–triplet energy transfer. Improvements in actual formulations may simultaneously arise from spectral load sharing, collisional quenching, changes in the solvent environment, and multicomponent energy-transfer processes.

The contribution of each mechanism in a specific formulation must be assessed using transient absorption spectroscopy, triplet-state lifetime measurements, and comparisons of absorption performance before and after irradiation.

4.2.3 Helping Increase the Solubility Margin and Reduce Crystallization Risk

Avobenzone is a solid crystalline UV filter. After sunscreen is applied to the skin, water and volatile components gradually evaporate, increasing the concentration of UV filters in the remaining oil phase. If the dissolving capacity of the oil phase is insufficient, avobenzone may nucleate and form crystals.

Crystallization may cause:

① nonuniform distribution of the UV filter within the film;

② increased ultraviolet transmittance in localized areas;

③ a reduction in the effective absorption area;

④ reduced film continuity and optical uniformity.

Octocrylene is a liquid with pronounced oil solubility. In suitable formulations, it can increase the solubility margin of avobenzone and delay crystallization during drying or low-temperature storage.

The improvement of avobenzone systems by octocrylene may involve spectral load sharing, excited-state processes, and solubility-state effects. Whether the finished product remains stable also depends on the UV-filter ratio, oil-phase composition, antioxidant system, film-forming structure, packaging, and storage conditions.

5 State of Octocrylene in the Film Formed on the Skin

5.1 Lipophilicity Is Not Equivalent to Independent Film Formation

After a sunscreen is applied, octocrylene is primarily present in the oil phase and the hydrophobic regions of the dried film. Because of its low water solubility, it is not readily dissolved directly by water and may contribute to the hydrophobicity of the film and the distribution of UV filters.

Octocrylene is a low-molecular-weight oily liquid rather than a typical polymeric film-forming agent. It lacks the long-chain polymeric structure required to form a strong continuous network and cannot independently produce a stable film resistant to water, perspiration, and abrasion.

The film formed by a sunscreen product generally consists of the following components:

① acrylates, polyurethanes, or other film-forming polymers;

② silicone oils, waxes, and high-viscosity oils;

③ emulsifiers and thickening networks;

④ organic UV filters and inorganic particles;

⑤ a multiphase composite structure formed after the product dries.

Octocrylene can be dispersed within this composite film and help maintain a uniform state of oil-soluble UV filters. Whether a product is water resistant must be determined through finished-product water-resistance testing and cannot be inferred solely from the presence of octocrylene in the formulation.

6 Dermal Absorption and Human Metabolism

6.1 Can Octocrylene Enter the Systemic Circulation?

Octocrylene is highly lipophilic and can enter the lipids of the stratum corneum. Entry into the stratum corneum is not equivalent to entry into the bloodstream. Only the portion that continues through the viable epidermis and dermis and reaches the capillaries constitutes systemic absorption.

Clinical trials organized by the U.S. Food and Drug Administration (FDA) showed that octocrylene could be detected in plasma after repeated, large-area application of sunscreen products containing octocrylene. Measurable concentrations were also observed after a single application of some test products.[4][5]

These results confirm that octocrylene can undergo percutaneous absorption. However, detection in the bloodstream does not mean that health damage has occurred. The FDA has stated that the studies did not conclude that the tested sunscreen ingredients were unsafe. Existing data remain insufficient to determine which levels of systemic exposure may be regarded as safe, and further information is therefore needed concerning the extent of absorption, clearance from the body, and the effects of long-term repeated exposure.

6.2 Metabolism after Entry into the Human Body

Human biomonitoring studies have identified multiple octocrylene metabolites in urine.[6][7]

The principal processes supported by current evidence include:

Octocrylene

↓ Ester-bond hydrolysis and/or side-chain oxidation

Metabolites including CDAA, 5OH-OC, and DOCCA

↓ Further oxidation and partial conjugation reactions

Free or conjugated metabolites

↓

Urinary excretion; part of the unrecovered dose may also be excreted through feces or other routes

Phase I metabolism includes ester-bond hydrolysis as well as hydroxylation and further oxidation of the 2-ethylhexyl side chain. In an oral human study, CDAA was the principal urinary metabolite, whereas the amounts of 5OH-OC and DOCCA excreted were comparatively lower. The conjugation patterns of the metabolites differed: CDAA was excreted mainly in its free form, whereas 5OH-OC was detected primarily as a glucuronide conjugate.[1][6][7]

Existing studies demonstrate that the human body can absorb, transform, and excrete a proportion of octocrylene. However, the quantitative contributions of individual metabolic pathways, tissue distribution, and kinetics following long-term repeated exposure remain areas for further investigation.

7 Environmental Fate and Ecological Risk

Octocrylene has low water solubility and high lipophilicity. Environmental monitoring studies have detected octocrylene in wastewater, surface water, coastal seawater, sediments, and biological tissues, including those of fish and corals. Based on its physicochemical properties and environmental monitoring data, octocrylene entering aquatic environments may partition into particulate matter, sediments, and lipid-rich biological tissues rather than remaining uniformly distributed in the aqueous phase for prolonged periods.[14][15]

The principal environmental input pathways include:

① release from the skin surface during swimming and other aquatic activities;

② domestic wastewater generated by bathing and cleansing;

③ product manufacturing and disposal;

④ entry of human metabolites into wastewater systems through excretion.

Experimental studies have found that octocrylene can form fatty-acid conjugates in the tissues of the coral Pocillopora damicornis and is associated with metabolic changes related to mitochondrial dysfunction.[9]

These studies indicate that octocrylene can be taken up and biotransformed by corals. However, actual marine environmental risk is also affected by environmental concentration, duration of exposure, water-exchange rate, species sensitivity, water temperature, and other pollutants. Effects observed under laboratory conditions cannot be directly regarded as representative of ecological outcomes in all natural waters.

Local exposure warrants greater attention in heavily visited coral-reef areas with limited seawater exchange. Palau, the U.S. Virgin Islands, and other jurisdictions have introduced restrictions on sunscreen products containing octocrylene. These measures are intended for aquatic ecosystem protection and use exposure subjects and risk indicators that differ from those applied in human cosmetic safety assessments.

8 Principal Regulatory Requirements

9 Representative Chemicals Related to Research on Octocrylene UV Absorption, Photochemical Cycling, and Formulation Stability

Table 1. Core UV Filters and Spectral Compatibility Controls

Table 2. Broad-Spectrum, Photostabilizing, and Inorganic UV Filters

Table 3. Compounds Related to Antioxidant Activity and Reactive-Species Detection

Table 4. Reference Compounds for Impurity Degradation and Photosensitization Studies

Note: The products listed above are representative Aladdin products related to scientific research, analytical testing, and formulation studies. The listed research reagents are not equivalent to cosmetic-grade raw materials. Their suitability for use in cosmetic formulations must be determined with consideration of raw-material grade, impurity control, particle size and surface treatment, applicable regulations, and finished-product safety assessment. Additional product specifications, grades, and Certificates of Analysis may be searched on the Aladdin website using the product name, CAS number, or catalog number.

References

[1] Scientific Committee on Consumer Safety. Opinion on Octocrylene (CAS No. 6197-30-4, EC No. 228-250-8), final version of 30–31 March 2021. SCCS/1627/21. European Commission, 2022. doi:10.2875/955656.

[2] Matsumura Y, Ananthaswamy H N. Toxic Effects of Ultraviolet Radiation on the Skin. Toxicology and Applied Pharmacology, 2004, 195(3): 298–308.

[3] Nash J F, Tanner P R. Relevance of UV Filter/Sunscreen Product Photostability to Human Safety. Photodermatology, Photoimmunology & Photomedicine, 2014, 30(2–3): 88–95.

[4] Matta M K, Florian J, Zusterzeel R, et al. Effect of Sunscreen Application on Plasma Concentration of Sunscreen Active Ingredients: A Randomized Clinical Trial. JAMA, 2020, 323(3): 256–267.

[5] U.S. Food and Drug Administration. Shedding More Light on Sunscreen Absorption. FDA, 2020.

[6] Bury D, Belov V N, Qi Y, Hayen H, Volmer D A, Brüning T, Koch H M. Determination of Urinary Metabolites of the Emerging UV Filter Octocrylene by Online-SPE-LC-MS/MS. Analytical Chemistry, 2018, 90(1): 944–951. doi:10.1021/acs.analchem.7b03996.

[7] Bury D, Modick-Biermann H, Leibold E, Brüning T, Koch H M. Urinary Metabolites of the UV Filter Octocrylene in Humans as Biomarkers of Exposure. Archives of Toxicology, 2019, 93(5): 1227–1238.

[8] Downs C A, DiNardo J C, Stien D, Rodrigues A M S, Lebaron P. Benzophenone Accumulates over Time from the Degradation of Octocrylene in Commercial Sunscreen Products. Chemical Research in Toxicology, 2021. doi:10.1021/acs.chemrestox.0c00461.

[9] Stien D, Clergeaud F, Rodrigues A M S, Lebaron K, Pillot R, Romans P, Fagervold S, Lebaron P. Metabolomics Reveal That Octocrylene Accumulates in Pocillopora damicornis Tissues as Fatty Acid Conjugates and Triggers Coral Cell Mitochondrial Dysfunction. Analytical Chemistry, 2019, 91(1): 990–995. doi:10.1021/acs.analchem.8b04187.

[10] China Food and Drug Administration. Safety and Technical Standards for Cosmetics (2015 Edition) [S]. China Food and Drug Administration Announcement No. 268 of 2015, issued December 23, 2015, effective December 1, 2016.

[11] European Parliament and Council of the European Union. Regulation (EC) No 1223/2009 on Cosmetic Products, Annex VI, consolidated version of 1 May 2026.

[12] U.S. Food and Drug Administration. An Update on Sunscreen Requirements: The Deemed Final Order and the Proposed Order. Content current as of December 16, 2022.

[13] Bundesinstitut für Risikobewertung. UV-Filtersubstanzen in Sonnenschutzmitteln. Stellungnahme des BfR vom 6. August 2003.

[14] Balmer M E, Buser H R, Müller M D, Poiger T. Occurrence of Some Organic UV Filters in Wastewater, in Surface Waters, and in Fish from Swiss Lakes. Environmental Science & Technology, 2005, 39(4): 953–962. doi:10.1021/es040055r.

[15] Mitchelmore C L, He K, Gonsior M, Hain E, Heyes A, Clark C, Younger R, Schmitt-Kopplin P, Feerick A, Conway A, Blaney L. Occurrence and Distribution of UV-Filters and Other Anthropogenic Contaminants in Coastal Surface Water, Sediment, and Coral Tissue from Hawaii. Science of the Total Environment, 2019, 670: 398–410. doi:10.1016/j.scitotenv.2019.03.034.

[16] Republic of Palau. Republic of Palau Public Law No. 10-30: Responsible Tourism Education Act of 2018. 2018.

[17] Legislature of the Virgin Islands. Act No. 8185, Bill No. 33-0043. 2019.

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