The routine exchange of currency means that coins and banknotes pass through countless hands, leading many people to wonder what microscopic life might be hitching a ride on their spare change. This natural public health concern has driven scientific inquiry to examine coins as potential carriers for bacteria and viruses. Findings confirm that currency does harbor microorganisms, but the specific material of coins introduces a unique factor into disease transmission.
What Microorganisms Are Found on Currency?
Scientific investigations consistently reveal a wide range of microbial contaminants on coins. Studies confirm they carry both common environmental bacteria and indicators of human contact. These microbes often include species like Staphylococcus aureus (commonly found on human skin) and Escherichia coli (which can indicate fecal contamination).
Researchers have also isolated other potentially harmful organisms from coins, such as Salmonella enterica and Klebsiella species. The type and amount of bacteria vary depending on the coin’s environment. Coins have even been found to harbor antibiotic-resistant bacteria, including Methicillin-resistant Staphylococcus aureus (MRSA) and Vancomycin-resistant Enterococcus (VRE).
Pathogen Viability on Metal Surfaces
The survival time of pathogens on coins is heavily influenced by the coin’s metallic composition, a phenomenon known as the oligodynamic effect. This effect describes the biocidal action of small quantities of certain metals, particularly copper and silver, which are toxic to microorganisms. Since many coins contain high percentages of copper, or are copper-plated, they possess inherent antimicrobial activity.
The copper in the metal alloy releases ions that interfere with the essential proteins and cell membranes of bacteria and viruses, effectively neutralizing them. Laboratory tests show that copper-containing coins can kill over 99.9% of bacteria like Staphylococcus aureus and E. faecium within 24 hours. This rapid die-off contrasts sharply with porous materials like paper banknotes, where bacteria can survive much longer. Although the topography of coins, with their scratches and crevices, can favor initial adhesion, the metal’s toxicity quickly limits multiplication.
Assessing the Actual Health Risk of Handling Coins
While coins are confirmed to carry potentially harmful microbes, the actual risk of disease transmission remains low for the general population. Infection requires a sufficient dose of a pathogen and a direct route of entry, such as touching the mouth, nose, or an open wound after handling the contaminated surface. The antimicrobial properties of the metals in coins reduce the number of viable pathogens, making the coin a relatively poor vector compared to porous materials or frequently touched objects like mobile phones.
A person with a healthy immune system is unlikely to become ill from the low number of viable organisms transferred from a coin. Public health officials have stated that coins do not pose a greater risk of transmitting viruses like COVID-19 than other common surfaces. Therefore, although coins are biologically “dirty,” they are not a primary driver of infectious disease spread, especially when compared to person-to-person contact.
Essential Hygiene Practices for Currency
Maintaining simple hygiene practices minimizes any potential risk associated with handling currency. The most effective step is to wash hands thoroughly with soap and water for at least 20 seconds immediately after handling coins. If soap and water are unavailable, use an alcohol-based hand sanitizer with at least 60% alcohol concentration.
It is important to consciously avoid touching the face, particularly the eyes, nose, and mouth, after exchanging money and before cleaning hands. These routine actions break the chain of contamination, preventing microbes picked up from coins from entering the body.