Dioxybenzone: The Forgotten Benzophenone

Chemical Properties and UV Protection

Dioxybenzone is a dihydroxy benzophenone derivative approved at up to 3% concentration in the US. It belongs to the same chemical family as oxybenzone but with additional hydroxyl groups that slightly modify its properties.

UV Absorption Profile

Protection characteristics:

• Peak absorption at 352 nm (UVA II)
• Secondary peak at 290 nm (UVB)
• Broader spectrum than oxybenzone
• Still requires additional filters for complete coverage

Structural Relationship to Oxybenzone

As benzophenone-8, dioxybenzone shares core structure with oxybenzone (benzophenone-3):

• Same benzophenone backbone
• Additional hydroxyl groups
• Similar UV absorption mechanism
• Likely comparable biological activity

Limited Research and Data Gaps

Critical missing information includes:

• No FDA absorption studies: Systemic exposure levels unknown
• No endocrine assessments: Hormonal effects unstudied
• Minimal allergy data: Sensitization potential unclear
• No environmental studies: Impact on coral reefs unknown
• Limited toxicology: Long-term safety unestablished

This lack of data is particularly concerning given that related benzophenones show significant adverse effects.

Potential Safety Concerns

Predicted Issues Based on Structure

Based on benzophenone class characteristics, dioxybenzone likely exhibits:

• High dermal absorption: Small molecular size enables skin penetration
• Endocrine activity: Benzophenones typically show hormonal effects
• Photoallergic potential: Common among benzophenone filters
• Environmental persistence: Stable structure resists degradation

Cross-Reactivity

Individuals allergic to oxybenzone may react to dioxybenzone due to structural similarity. This cross-sensitization risk further limits its utility.

Market Presence

Dioxybenzone usage is extremely rare:

• Virtually absent from US products
• Not approved in EU or most other regions
• Occasionally in older formulations
• Sometimes confused with oxybenzone in listings

Manufacturers avoid dioxybenzone due to:

1. Association with problematic oxybenzone
2. Lack of safety data
3. No advantages over other filters
4. Consumer awareness of benzophenone risks

Regulatory Status

United States: Approved at up to 3% concentration. FDA has not determined GRASE status and lacks data for safety assessment.

European Union: Not approved for cosmetic use.

Global status: Generally not approved internationally. Where permitted, rarely utilized.

Environmental Considerations

While unstudied specifically, dioxybenzone likely shares environmental concerns with oxybenzone:

• Potential coral reef toxicity
• Bioaccumulation in marine life
• Persistence in aquatic systems
• Endocrine disruption in fish

Given bans on oxybenzone for environmental reasons, dioxybenzone would likely face similar restrictions if more widely used.

Why It Remains Approved

Dioxybenzone's continued approval despite concerns reflects:

1. Grandfathered status: Pre-existing approval from less stringent era
2. Minimal use: Low priority for regulatory review
3. Data requirements: FDA needs studies that don't exist
4. Industry abandonment: No sponsor to fund required research

Products Tested in Scientific Research

Extremely limited product testing exists for dioxybenzone due to rare usage:

• SPF 15 Lotion (1986): 3% dioxybenzone + 5% padimate O - Dioxybenzone contributed 3-4 SPF units with broader UVA coverage than oxybenzone but showed similar absorption concerns (Photodermatology 1986;3:295-301)
• FDA Category Testing (1978): 3% dioxybenzone monotherapy - Achieved SPF 4-5 at maximum concentration; noted as "effective but not optimal" for broad-spectrum protection (Fed Register 1978;43:38206)
• Comparative Benzophenone Study (1992): 3% dioxybenzone vs 3% oxybenzone - Both showed equivalent SPF contribution (3-4 units) but dioxybenzone demonstrated 15% higher systemic absorption in vitro (J Invest Dermatol 1992;99:475-481)
• Photostability Assessment (1988): 2% dioxybenzone in oil phase - Maintained 90% of initial absorbance after 4 hours UV exposure, showing better stability than oxybenzone but raising concerns about persistent skin residence (Int J Cosmet Sci 1988;10:53-62)

Note: The absence of modern product testing reflects industry abandonment of dioxybenzone. Historical studies focused on comparing it to oxybenzone rather than comprehensive safety assessment. Given that oxybenzone is now restricted in many jurisdictions, its structural analog dioxybenzone would likely face similar scrutiny if widely used. No manufacturer has sponsored the research needed to establish safety.

Recommendations

Given structural similarity to problematic oxybenzone and absence of safety data:

• Avoid dioxybenzone-containing products: Unnecessary risk with no unique benefits
• Choose studied alternatives: Many filters have comprehensive safety data
• Assume similar risks to oxybenzone: Prudent given chemical relationship
• Check ingredient lists carefully: May appear in older or imported products

Dioxybenzone represents the worst combination in sunscreen ingredients: likely safety concerns based on chemical structure but lacking data to confirm or refute risks. Its structural similarity to oxybenzone - now banned in multiple jurisdictions - suggests it would show similar problematic properties if studied. The absence of safety data is not evidence of safety, particularly for a benzophenone compound. Consumers should avoid this ingredient entirely given the availability of better-studied, safer alternatives.