Sulisobenzone Safety: Cleared in Europe, Open in the US

Is Sulisobenzone Safe? The Short Answer

Two regulators have looked at benzophenone-4 recently and given two different kinds of answer.

• European Union — safe at up to 5%. The Scientific Committee on Consumer Safety assessed it as a suspected endocrine disruptor and concluded, in a final opinion adopted on 27 March 2024, that "benzophenone-4 is safe when used as UV filter up to a maximum concentration of 5% in sunscreen, face and hand cream, all leave-on and rinse-off products (total dermal aggregate), lipstick, sunscreen propellant spray and pump spray." On the specific question it was asked, the committee recorded "no indications of endocrine activity", and found benzophenone-4 not phototoxic, not photosensitising, not photomutagenic, with "no in vitro genotoxic potential" and a very low risk of sensitisation in humans. It noted no carcinogenicity data.
• United States — still undecided. The FDA has proposed Category III for sulisobenzone: "The public record does not contain sufficient data to support a positive GRASE determination for … sulisobenzone … at this time." The 2021 proposed order that replaced the 2019 rulemaking proposes requirements "substantively the same" as the 2019 rule, with scientific discussions that "are generally the same" — and neither has been finalized, so sulisobenzone remains legal at up to 10%.

The US gap is specific and it is about absorption. Sulisobenzone has been studied in laboratory skin-penetration work — the FDA records that those studies show it permeating into the epidermis and dermis, with the vehicle and companion actives able to increase that penetration, and the EU's review put the figure at 0.20% ± 0.13% of an applied dose in a human-skin test. What does not exist is the other half: of the ten filters with the biggest gaps, only homosalate, octinoxate and octisalate "appear to have been evaluated in human absorption studies," and none of the ten has been through an adequate maximal-usage trial. Nor was sulisobenzone covered by the deferral request the FDA received for eight ingredients.

The family resemblance is worth stating precisely. Benzophenone-4 is benzophenone-3 — oxybenzone — with a sulfonic acid group bolted on to make it water-soluble. That is a reason the EU put it on its endocrine-disruptor priority list; it is not a finding. The review that followed did not carry oxybenzone's problems across, sulisobenzone has its own approval and its own limits, and reef bans written against oxybenzone do not name it.

Chemical Properties and UV Protection

Sulisobenzone is benzophenone-4, created by adding a sulfonic acid group to the benzophenone structure. Approved at up to 10% concentration in the US, it's designed for water-based and beach-resistant formulations.

UV Absorption Spectrum

Protection profile similar to oxybenzone:

• Absorption maximum at 288 nm (UVB), per the EU's 2024 safety review
• Absorbs into the shorter UVA (UVA II) range as well
• Requires high concentrations for efficacy

Water Solubility Implications

The sulfonic acid group creates unique properties:

• Enables clear, water-based formulations
• May enhance skin penetration
• Increases environmental mobility
• Washes off more readily, reducing protection

Systemic Absorption Concerns

While not included in FDA absorption studies, structural analysis suggests:

• Enhanced penetration: Water solubility may increase dermal absorption
• Ionic nature: Sulfonate group could facilitate cellular uptake
• Systemic distribution: Water solubility enables wider tissue distribution
• Renal excretion: May accumulate in kidneys during elimination

Structural Similarity to Oxybenzone

Oxybenzone shows the highest absorption of any filter the FDA has tested — over 400 times its 0.5 ng/mL threshold. Sulisobenzone has never been put through the same trial, so no comparable figure exists for it. The in vitro human-skin work the EU relied on found about 0.20% of an applied dose crossing the skin, which does not support assuming oxybenzone-like exposure.

Endocrine Disruption Potential

Limited specific research exists, but benzophenone structure predicts:

• Estrogenic activity similar to oxybenzone
• Anti-androgenic effects
• Thyroid hormone interference
• Potential reproductive impacts

Water solubility may alter tissue distribution compared to oxybenzone, potentially affecting different organ systems or showing different accumulation patterns.

Environmental Concerns

Enhanced Environmental Mobility

Sulisobenzone's water solubility creates greater environmental risks:

• Readily washes off swimmers into water
• Highly mobile in aquatic systems
• Difficult to remove in wastewater treatment
• May contaminate drinking water sources
• Potentially higher bioavailability to aquatic organisms

Marine Toxicity

While less studied than oxybenzone, sulisobenzone likely shares coral toxicity concerns:

• Same benzophenone core structure
• Enhanced water solubility increases exposure
• May be included in future reef-safe bans

Limited Market Presence

Sulisobenzone usage remains minimal:

• Rarely used in US products
• Not approved in many countries
• Sometimes in hair care products with SPF
• Occasionally in water-resistant formulas

Manufacturers avoid sulisobenzone due to:

1. Association with problematic benzophenones
2. Consumer awareness of oxybenzone risks
3. Availability of better alternatives
4. Formulation challenges

Regulatory Status

United States: Approved at up to 10% concentration. FDA has not determined GRASE status, lacking sufficient safety data.

European Union: Approved at up to 5% (acid or salts).

Global perspective: Limited international approval and usage.

Unique Risks of Water Solubility

Sulisobenzone's water solubility creates distinct concerns:

For Human Health

• May penetrate skin more readily than oil-soluble filters
• Could reach systemic circulation faster
• Different organ distribution than lipophilic compounds
• Potential kidney accumulation during excretion

For Environment

• Immediate release into water bodies
• Spreads rapidly through aquatic ecosystems
• Cannot be contained or filtered easily
• May contaminate groundwater

Comparison to Oxybenzone

Recommendations

Given structural similarity to oxybenzone and unique water-solubility risks:

• Avoid sulisobenzone-containing products: Benzophenone risks plus water-solubility concerns
• Choose mineral alternatives: Provide protection without absorption or environmental mobility
• Be cautious with water-based SPF products: May contain sulisobenzone or similar compounds
• Check hair care products: Sometimes hidden in leave-in treatments with SPF

Sulisobenzone combines the worst aspects of chemical sunscreens: the benzophenone structure associated with high absorption and endocrine disruption, plus water solubility that enhances environmental contamination and potentially increases bioavailability. While specific studies are limited, the structural relationship to oxybenzone - now banned in multiple jurisdictions - suggests similar safety concerns. The added water solubility creates unique risks for both human health and environmental contamination. Consumers should avoid this ingredient, particularly given the availability of safer, more effective alternatives.

Recommended: EltaMD UV Pure SPF 47 — a sulisobenzone-free alternative — 100% mineral, water resistant