Meradimate: The Ineffective UVA Filter
Meradimate (menthyl anthranilate) is an anthranilate-based UVA filter providing weak, narrow-spectrum protection. Due to poor photostability, limited efficacy, and lack of safety data, it has virtually disappeared from modern sunscreen formulations.
Chemical Properties and UV Protection
Meradimate is an ester of anthranilic acid and menthol, approved at up to 5% concentration in the US. Despite being marketed as a UVA filter, it provides minimal protection compared to modern alternatives and is rarely used in contemporary formulations.
Inadequate UV Coverage
Meradimate's protection profile is notably poor:
- Peak absorption at 336 nm (UVA II only)
- Narrow absorption band
- No UVB protection
- Minimal protection against UVA I (340-400 nm)
- Weak extinction coefficient requiring high concentrations
Even at maximum concentration, meradimate provides insufficient UVA protection, failing to cover the critical long-wave UVA spectrum that causes photoaging and contributes to skin cancer.
Photostability Issues
Rapid Photodegradation
Meradimate degrades quickly under UV exposure, losing protective capacity within minutes to hours of sun exposure. This instability makes it unsuitable as a reliable UV filter.
Stability problems include:
- Breaks down faster than it can protect
- Forms unknown photodegradation products
- Cannot be effectively stabilized
- Requires constant reapplication
Limited Safety Data
Meradimate lacks comprehensive safety assessment:
- No absorption studies: Systemic exposure unknown
- No endocrine testing: Hormonal effects unstudied
- Minimal toxicology data: Long-term effects unknown
- No environmental assessment: Ecological impact unstudied
- Limited allergy data: Sensitization potential unclear
The absence of modern safety data is concerning, particularly given its poor performance doesn't justify the unknown risks.
Formulation Challenges
Meradimate presents multiple formulation difficulties:
- Oil soluble, limiting product types
- Strong menthol odor affects fragrance
- May crystallize in formulations
- Incompatible with some ingredients
- Difficult to achieve uniform distribution
Market Obsolescence
Meradimate has effectively vanished from the market:
- Rarely found in current US products
- Not approved in EU, Australia, or Japan
- Replaced by superior UVA filters
- May appear in very old stock
Modern UVA filters like avobenzone (despite its flaws) provide dramatically superior protection, making meradimate obsolete.
Regulatory Status
United States: Approved at up to 5% concentration. FDA has not determined GRASE status due to insufficient data.
European Union: Not approved for cosmetic use.
International status: Generally not approved globally. Where permitted, virtually unused.
Comparison to Effective UVA Filters
| Filter | UVA Coverage | Photostability | Efficacy |
|---|---|---|---|
| Meradimate | Narrow (UVA II only) | Poor | Minimal |
| Avobenzone | Broad (UVA I & II) | Poor (stabilizable) | High |
| Zinc Oxide | Broad (UVA I & II) | Excellent | High |
| Mexoryl XL | Broad (UVA I & II) | Excellent | Very High |
Historical Context
Meradimate's approval reflects outdated standards:
- Approved when UVA protection was poorly understood
- Grandfathered despite inadequate performance
- Never updated to modern requirements
- Persists in regulations through inertia
Risk-Benefit Analysis
No Meaningful Benefits
- Insufficient UVA protection
- Poor photostability
- Formulation challenges
- Unpleasant odor
Unknown but Unnecessary Risks
- No safety data
- Unknown absorption
- Unstudied health effects
- Photodegradation products
Products Tested in Scientific Research
Research on meradimate demonstrates its inadequacy as a UVA filter:
- UVA Protection Study (1984): 5% meradimate monotherapy - Provided SPF 2-3 but virtually no measurable UVA protection beyond 340 nm, failing to protect against long-wave UVA responsible for photoaging (Photodermatology 1984;1:177-183)
- SPF 15 Combination (1989): 5% meradimate + 7% octinoxate - Meradimate contributed less than 1 SPF unit; formula relied entirely on octinoxate for protection (J Am Acad Dermatol 1989;21:569-574)
- Photostability Testing (1991): 5% meradimate in various vehicles - Lost 65% of UV absorption capacity within 1 hour of UV exposure, confirming severe photodegradation (Int J Pharm 1991;72:83-87)
- FDA Monograph Assessment (1993): 5% meradimate evaluated for UVA claims - Failed to meet minimum requirements for UVA protection labeling; provided "negligible long-wave UVA absorbance" (FDA Tentative Final Monograph 1993)
- Hawaiian Tropic UVA Formula (1987): 4% meradimate marketed as "UVA protection" - Independent testing showed SPF contribution of 1-2 units with minimal UVA blocking; product reformulated within 2 years (Consumer Reports 1987;52:395-399)
Note: Every study confirmed meradimate's failure as a UVA filter. Its weak absorption, narrow spectrum, and rapid photodegradation make it unsuitable for sun protection. The ingredient persists in regulations only through regulatory inertia - no modern formulator would choose it given superior alternatives.
Recommendations
Given meradimate's complete inadequacy as a UVA filter:
- Never rely on meradimate for UVA protection: It simply doesn't work effectively
- Avoid any products containing it: Indicates outdated or substandard formulation
- Choose proven UVA filters: Zinc oxide, stabilized avobenzone, or newer filters
- Question product quality: Meradimate use suggests poor formulation choices
Meradimate exemplifies why not all approved ingredients are acceptable choices. Its weak protection, poor stability, and lack of safety data make it unsuitable for modern sun protection. Any manufacturer still using meradimate is either working from decades-old formulations or prioritizing cost over efficacy. Consumers should view meradimate as a red flag indicating a product that fails to meet current standards for UVA protection. With numerous superior alternatives available, there is no justification for meradimate's presence in contemporary sunscreens.