Copper vs. Silver – which is the best antimicrobial?

While Silver’s antimicrobial properties are widely acknowledged, it’s often overlooked that both Copper and Gold possess similar capabilities. These three elemental metals exhibit what’s known as “the Oligodynamic effect,” a phenomenon identified over 150 years ago. This effect highlights the biocidal nature of certain metal ions, capable of inhibiting the growth of microorganisms even at very low concentrations. Essentially, these metals release ions that bind covalently to proteins, disrupting the functionality and replication of microorganisms.

In addition to the Oligodynamic ionic effect, Copper employs various other mechanisms to combat microbes. In specific formulations, such as those utilized by Cupron in its active additives, Copper releases electrons, generating reactive oxygen species that wreak havoc on viruses, fungi, and bacteria. This multi-pronged assault on microorganisms includes plasma membrane permeabilization, membrane lipid peroxidation, damage to nucleic acids, and inhibition of intracellular protein assembly and activity (Borkow G.; Gabbay J. Copper as a biocidal tool. Curr Med Chem 2005, 12(18), 2163-2175).

The combination of these multisite, non-specific damaging mechanisms makes it exceptionally challenging for microorganisms to develop tolerance to Copper. Consequently, the prevalence of Copper-tolerant microorganisms remains remarkably low (Borkow G.; Gabbay J. Copper as a biocidal tool. Curr Med Chem 2005, 12(18), 2163-2175; Giachino A.; Waldron K.J. Copper tolerance in bacteria requires the activation of multiple accessory pathways. Mol Microbiol 2020, 114(3), 377-390.). You can read more about how copper kills here.

Microorganisms employ various strategies to regulate intracellular copper levels, primarily through the use of copper chaperones and specific copper efflux pumps (Rademacher C.; Masepohl B. Copper-responsive gene regulation in bacteria. Microbiology 2012, 158, 2451-2464; Dennison C.; David S.; Lee J. Bacterial copper storage proteins. J Biol Chem 2018, 293, 4616-4627). However, when faced with an excessive concentration of copper—varying among different microorganisms— they cannot cope with the excess copper and are killed (Borkow G. Using copper to fight microorganisms. Curr Chem Biol 2012, 6(2), 93-103; Reyes-Jara A, et al. Antibacterial Effect of Copper on Microorganisms Isolated from Bovine Mastitis. Front Microbiol 2016, 7, 626).

Moreover, Copper stands out as the sole metal possessing antimicrobial properties while also serving as an essential micronutrient for humans (and all other living organisms) (Uauy R, Olivares M, Gonzalez M. Essentiality of copper in humans. Am J Clin Nutr. 1998;67(5 Suppl):952S-959S). Its indispensability extends to crucial functions such as cell respiration, neurotransmitter synthesis, and the formation of collagen and elastin in the skin. While high concentrations of Copper can indeed pose toxicity risks, it generally presents fewer environmental concerns compared to other metals. According to the EPA, the toxicity of Silver exceeds that of Copper by a staggering 65-fold.

Lastly, and most significantly, Copper demonstrates superior effectiveness across a broader spectrum of conditions, outperforming Silver in environments where Silver’s efficacy diminishes (Michels, H.T., et al. (2009) Effects of temperature and humidity on the efficacy of methicillin-resistant Staphylococcus aureus challenged antimicrobial materials containing silver and copper Lett Appl Microbiol 49(2):191-5; Minoshimaa M., et al. Comparison of the antiviral effect of solid-state copper and silver compounds. Journal of Hazardous Materials 312 (2016) 1–7; Borkow, G., Roth, T., Kalinkovich, A. (2022) Wide Spectrum Potent Antimicrobial Efficacy of Wound Dressings Impregnated with Cuprous Oxide Microparticles. Microbiol. Res. 13(3), 366-376). While Silver’s performance may falter under hot and humid conditions, Copper maintains its efficacy across various temperatures and humidity levels (Michels, H.T., et al. (2009) Effects of temperature and humidity on the efficacy of methicillin-resistant Staphylococcus aureus challenged antimicrobial materials containing silver and copper Lett Appl Microbiol 49(2):191-5).

Here’s a table summarizing the key differences, with references.

	Feature	Copper	Silver
1	EPA Public Health Claims	Multiple1	Minimal2
2	Efficacy	Broad spectrum (Bacteria, Viruses & Fungi & Fungal Spores)3	Less effective against Viruses; Fungi & Fungal spores4
3	Mode of action	Metal ion5 Reactive Oxygen Species7	Metal ion6
4	Role in Human body	Essential micronutrient8 Improves skin elasticity9 Enhances wound healing10	None
5	Durability	High, due to low solubility	Depends on type of treatment but not as durable
6	Sweaty Environment	Enhances efficacy11	Diminishes efficacy12
7	Temperature	Maintains Efficacy1314	Low temperature reduces efficacy15
8	Humid Environment	Maintains Efficacy16	Low humidity reduces efficacy17