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2,2'-THIOBIS(4-CHLOROPHENOL).

Avoid CAS 97-24-5 / ANTIMICROBIAL

A chlorinated phenolic antimicrobial compound historically used in topical formulations for its broad-spectrum fungistatic and antibacterial properties. Also known as Fenticlor, this ingredient disrupts microbial cell membranes but carries significant photoallergenic risks that limit its modern cosmetic applications.

Antimicrobial Fungistatic Preservative

Science

Penetrates microbial cell walls and disrupts cytoplasmic membranes by increasing proton permeability, dissipating the proton motive force required for cellular energy production and ultimately causing cell death through leakage of intracellular contents


Research

Medium confidence
Effective range 0.1–0.4%
Optimal

0.25%

Key findings

  1. 01 EPA documentation shows 0.1-0.4% provides effective antimicrobial activity in cosmetic formulations
  2. 02 UK regulatory data indicates 1.0% concentration effective for topical infections but associated with photoallergic reactions

Transparency

Not commonly dusted
Min. effective
0.05%
Red flag below
0.1%

Rarely used in modern cosmetics due to photoallergenic potential; any presence above 0.05% suggests intentional antimicrobial inclusion rather than trace contamination


The Formula

Solubility
Both
Optimal pH 4 – 7
0 7 14

Stability

Maintains structural integrity as solid but undergoes photodegradation with yellowing in solution when light-exposed; maximum antimicrobial efficacy achieved below pH 7.9 in un-ionized state

Conflicts

  • Anionic surfactants and emulsifiers
  • Oxidizing preservatives
  • Acidic actives
  • Formaldehyde donors
  • Retinoid formulations

Safety

CIR Status
Not reviewed
Max tested
0.4%
Pregnancy
Caution
Sensitization risk High

Classified as known photoallergen in dermatological testing; highly restricted in cosmetic applications with regulatory preference for safer alternative preservatives



Our Assessment

Avoid

Effective antimicrobial agent with unacceptable photoallergenic risk profile for modern precision skincare formulations.


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