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Moumoujus

THIMEROSAL.

Avoid CAS 54-64-8 / PRESERVATIVE

Thimerosal is an organomercury compound historically employed as a potent antiseptic and antifungal agent, primarily recognized for its role as a preservative in multi-dose vaccines. Despite its broad-spectrum antimicrobial activity, its application in skincare is severely limited by significant safety concerns, including high irritancy, accumulation potential, and neurotoxicity.

Summary

Antiseptic Antifungal Preservative

Science

Mechanism of Action

While its precise dermatological mechanism remains under investigation, Thimerosal exerts its effects by inhibiting the active sites of various sulfhydryl-containing enzymes and binding to sulfhydryl compounds, such as glutathione and cysteine. It also influences cellular calcium signaling by activating the InsP3 calcium channel, which can modulate numerous cellular functions, contributing to its antiseptic and antifungal properties via an oligodynamic effect.

Research

Clinical Evidence

Low confidence
Effective range N/A
Optimal

N/A

Transparency

Dusting Analysis

Not commonly dusted
Min. effective
Due to its significant toxicity and adverse reactions, any concentration beyond trace amounts is concerning. The FDA's limit for eye cosmetics is 0.0065%, but topical antibiotics containing Thimerosal have been banned.%
Red flag below
Any detectable concentration in general skincare applications is a significant red flag due to its severe safety profile. Specifically, a concentration of 0.0065% is the absolute maximum allowed in the eye area only, and 1% has shown local skin irritation.%

Thimerosal is not commonly 'dusted' into modern skincare formulations because the FDA banned its use in topically applied antibiotics in the 1980s due to severe skin reactions. It is largely phased out of cosmetics in both the EU and globally, with its permitted use extremely restricted to specific eye-area applications at very low concentrations (0.0065%). Its known potential for accumulation and toxicity makes it unsuitable for general cosmetic inclusion.

The Formula

Formulation

Solubility
Unknown
Optimal pH N/A
0 7 14

Conflicts

  • Aluminum (potential for chemical interaction and skin burns)
  • Other mercury-containing compounds (risk of cross-reactions)

Safety

Safety Profile

CIR Status
Not reviewed
Max tested
0.0065%
Pregnancy
Caution
Sensitization risk High

The FDA has prohibited the sale of topically applied Thimerosal antibiotics due to severe adverse skin reactions. As a mercury compound, it is readily absorbed through the skin and can accumulate, potentially inducing allergic reactions, irritation, and neurotoxic effects. While restricted to 0.0065% (65 ppm) in eye-area cosmetics in the US, and regulated as a preservative in the EU (though practically no longer used), its sensitizing potential is widely acknowledged by health authorities including WHO.

Your Skin

Skin Compatibility

No Normal
No Dry
No Oily
No Sensitive
Irritancy High
Comedogenicity Unknown

Our Assessment

Verdict

Avoid

Thimerosal presents significant safety concerns including high irritancy, systemic absorption, accumulation, and neurotoxic potential, rendering it unsuitable and highly discouraged for skincare formulations.

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References

Sources