Zinc Pyrithione (ZnPT) CAS 13463-41-7
Zinc Pyrithione (ZnPT): Properties, Applications, and Safety
1. Introduction
Zinc pyrithione (ZnPT) is a coordination complex of zinc with pyrithione ligands, widely recognized as an effective antifungal and antibacterial agent. It is best known as the active ingredient in over‑the‑counter antidandruff shampoos and treatments for seborrheic dermatitis. Beyond personal care, ZnPT is also used in paints, coatings, and industrial products as a preservative and antifouling agent. Its broad‑spectrum antimicrobial activity, low solubility in water, and stability make it a versatile biocide.
2. Chemical Structure and Properties
Molecular formula: C₁₀H₈N₂O₂S₂Zn
Molecular weight: 317.70 g/mol
CAS number: 13463-41-7
EC number: 236-671-3
Appearance: White to yellowish crystalline powder
Melting point: Approximately 240°C (decomposes)
Solubility: Practically insoluble in water (6–8 mg/L at neutral pH); sparingly soluble in organic solvents; soluble in DMSO
Stability: Hydrolysis‑stable across a range of pH values (4–8); sensitive to light and heat; forms insoluble precipitates with cationic and non‑ionic surfactants
3. Mechanism of Antimicrobial Action
ZnPT exerts its antimicrobial effects through multiple mechanisms:
Membrane disruption: ZnPT disrupts microbial cell membranes by blocking proton pumps, leading to impaired membrane transport and cellular dysfunction.
Copper ionophore activity: ZnPT acts as a copper ionophore, delivering copper ions into fungal cells. The increased intracellular copper damages iron‑sulfur clusters in essential metabolic proteins, inhibiting fungal growth and viability.
Enzyme inhibition: ZnPT inhibits the activity and expression of enzymes critical for the survival and virulence of fungi such as Malassezia.
Zinc‑mediated effects: The zinc component contributes to the overall biocidal activity, although the primary mechanism is attributed to the pyrithione ligand and its ionophore properties.
4. Applications
Cosmetics and personal care: ZnPT is used in antidandruff shampoos, conditioners, and scalp treatments at concentrations of 0.5–1.0% to control flaking, itching, and inflammation associated with dandruff and seborrheic dermatitis. It is also found in some topical creams and lotions.
Paints and coatings: Used as a preservative and antifouling agent in exterior paints, marine coatings, and wood preservatives to prevent mold, mildew, and algal growth.
Industrial products: Added to metalworking fluids, adhesives, and textiles as a biocide to prevent microbial contamination.
5. Safety and Toxicology
Human safety: ZnPT is generally considered safe at recommended concentrations in rinse‑off products. It may cause mild skin irritation in some individuals; contact with eyes should be avoided.
Regulatory status: In the EU, ZnPT has been classified as Repr 1B (potentially reproductively toxic). As of March 2022, its use in leave‑on cosmetic products is banned under EU Regulation 2021/1902; it remains permitted in rinse‑off products up to 1%. In the US, ZnPT is approved as an over‑the‑counter (OTC) active ingredient for antidandruff use under FDA monograph.
Environmental impact: ZnPT is highly toxic to aquatic organisms and has been shown to accumulate in aquatic environments, particularly in waters with limited sunlight. Its widespread use has raised concerns about ecological effects on fish, crustaceans, and other marine life.
6. Conclusion
Zinc pyrithione (CAS 13463-41-7) remains a widely used and effective antifungal and antibacterial agent, particularly in antidandruff shampoos and personal care products. Its broad‑spectrum activity, low water solubility, and stability make it suitable for various applications, including paints and industrial biocides. However, regulatory restrictions in the EU and growing environmental concerns regarding aquatic toxicity highlight the need for careful risk management and continued research into safer alternatives. When used within approved concentrations and applications, ZnPT provides reliable antimicrobial protection with an acceptable safety profile for human use.