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PHENYLBENZIMIDAZOLE SULFONIC ACID.

Valuable CAS 27503-81-7 / LIGHT STABILIZER, UV ABSORBER, UV FILTER

Phenylbenzimidazole Sulfonic Acid, also known as Ensulizole, is a water-soluble UV filter engineered to absorb harmful UVB radiation. It effectively stabilizes formulations, offering reliable sun protection with a typically low risk of skin irritation and pore-clogging.

Summary

UV filter Light stabilizer UV absorber

Science

Mechanism of Action

This ingredient operates by forming a uniform, protective film on the stratum corneum, the skin's outermost layer. It primarily functions as a UVB filter, efficiently absorbing incident light energy within the 280-320 nm range, with peak protection observed at 306 nm. The absorbed UV energy is then safely dissipated as heat, preventing photons from reaching deeper skin layers. This action safeguards keratinocytes from oxidative damage and DNA alterations. Furthermore, Phenylbenzimidazole Sulfonic Acid exhibits excellent photostability, ensuring consistent protective performance over time, and can enhance the stability of other less stable UV filters like avobenzone.

Research

Clinical Evidence

Medium confidence
Effective range 1–8%
Optimal

N/A

Key findings

  1. 01 Clinical assessments indicate a significant SPF protection potential, with studies suggesting a contribution of 2 SPF units per percent of the ingredient.
  2. 02 In vitro studies at 4 mM (significantly below FDA authorized concentrations) confirmed protection against cyclobutane pyrimidine dimers after UVB exposure. However, these studies also noted photosensitization leading to the formation of oxidized guanine bases upon UVA or UVB irradiation.

Transparency

Dusting Analysis

Not commonly dusted

The Formula

Formulation

Solubility
Water
Optimal pH 6.8 – 7.2
0 7 14

Stability

Phenylbenzimidazole Sulfonic Acid is inherently photostable, contributing to sustained protective efficacy under sun exposure. To achieve full solubilization in aqueous formulations, particularly for its free acid form, it requires neutralization with a base to a pH above 7, ideally within the precise range of 6.8 to 7.2.

Synergies

  • Enhances the photostability and reduces degradation of less stable oil-soluble UV filters, such as avobenzone.

Safety

Safety Profile

CIR Status
Safe as used
Max tested
8%
Sensitization risk Low

Generally regarded as safe for use in cosmetic and sunscreen formulations at concentrations up to 8.0%, as confirmed by regulatory bodies like the Scientific Committee on Consumer Products (SCCP). It demonstrates low potential for irritation to skin and conjunctiva, and importantly, is devoid of photo-irritating, phototoxic, or photoallergenic properties. While exhibiting low skin sensitization potential, sensitive individuals may rarely experience mild and transient skin reactions such as redness or itching. Direct eye contact should be avoided due to potential irritation. In vitro mutagenicity tests have shown no mutagenic or photomutagenic potential, and it is not classified as a CMR substance under EU Cosmetics Regulation.

Your Skin

Skin Compatibility

Yes Normal
No Dry
Yes Oily
Yes Sensitive
Irritancy Low
Comedogenicity Low

Our Assessment

Verdict

Valuable

As a photostable, water-soluble UVB filter demonstrating low irritancy and comedogenicity, Phenylbenzimidazole Sulfonic Acid is a valuable ingredient for effective, accessible sun protection across most skin types, when utilized within its authorized concentration limit.

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