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How dirty is American money?

American paper currency is widely used and exchanged daily. But how clean is all that cash? Research shows that paper money can harbor bacteria and viruses. The lifespan and high circulation of banknotes means they pass through many hands and locations, allowing microbes to attach and accumulate over time. But how serious is this as a public health issue? And does the material or denomination of the banknote affect the level of contamination? Let’s explore what studies reveal about how dirty American money really is.

How do microbes get onto money?

Paper money can become contaminated in a variety of ways:

  • Handling by many people – Bills pass between countless individuals. Microbes are transferred from hands to surfaces.
  • Contact with common surfaces – Bills are placed on dirty countertops, gas station pumps, vending machines etc where they pick up microbes.
  • Soil and dirt – Money dropped on floors collect microorganisms. Bills may literally be “dirty money”.
  • Bodily secretions – Mucus, sweat, saliva etc contain bacteria and viruses that can transfer to cash.
  • Improper storage – Storing money in unsanitary locations exposes it to contamination.

The more a banknote is handled, the greater the accumulation of microbes that may potentially transfer to each new handler.

Do different denominations show different contamination levels?

The value of the banknote doesn’t appear to significantly impact the level of microbial contamination.

Several studies have analyzed and compared samples from paper bills of various denominations ranging from $1 to $100. The general results showed no major differences in the total bacteria population levels between denominations.

This suggests that the degree of usage and handling is more important than the actual dollar value. Lower denominations like $1 are not necessarily dirtier than higher values like $20 despite being exchanged more frequently. The overall lifespan and number of exchanges facilitates bacterial accumulation regardless of specific denomination.

However, some early studies hypothesized that higher denominations may harbor certain bacteria species from hands more readily than lower values based on perceived differences in handling. But more extensive testing would be needed to demonstrate a definitive relationship.

How long do bacteria survive on banknotes?

The lifespan of microbes on paper money varies by specific type. Certain hardy species can potentially survive for extended periods during circulation.

In lab testing, pathogens like staphylococcus aureus, escherichia coli, and salmonella typhii have remained viable on banknote surfaces for days or even weeks. Fungi also demonstrate resilience.

However, survival also depends on environmental factors. Bacteria perish more quickly at higher temperatures and lower humidity. Normal pocket and wallet conditions provide greater longevity compared to harsher settings.

The polymer material in newer banknotes may inhibit microbial growth and survival versus cotton-paper bills. But polymer notes can still harbor bacteria in any crevices or indentations where dirt collects. Proper cleaning is required to fully sanitize currency.

How does U.S. money compare to foreign currencies in contamination?

Studies analyzing randomly sampled paper money from various countries consistently show widespread presence of microbes. Cash handled by the public intrinsically becomes a vehicle for biological transfer.

U.S. currency does not appear significantly dirtier than foreign paper money on average based on total bacteria counts. Contamination levels largely correlate to usage and soilage rather than any nation-specific traits or currency materials. Relative cleanliness depends more on hygiene habits of local populations.

However, U.S. coins may offer comparatively less microbe exposure than paper bills and other countries’ coins based on metal composition. But banknotes exhibit extensive contamination worldwide.

Bacteria species commonly found on U.S. banknotes

Researchers have identified a diverse mixture of microorganisms hitchhiking on U.S. paper money through culture and genetic analysis. Commonly detected bacteria include:

Gram-positive species

  • Staphylococcus – Often pathogenic and antibiotic resistant strains from human contact.
  • Streptococcus
  • Bacillus – Resilient spore-forming types able to survive harsh conditions.
  • Clostridium
  • Micrococcus – Common skin commensal bacteria.

Gram-negative species

  • Escherichia coli – Found in contaminated water and feces.
  • Klebsiella – Opportunistic pathogen originating from mouth, skin and intestines.
  • Pseudomonas – Ubiquitous environmental species.
  • Salmonella – Causes food poisoning and enteric fever.
  • Proteus – Common in spoiled organic matter.

Other types

  • Bacillus subtilis – Hardy spore-forming bacterium.
  • Listeria – Causes listeriosis infection from contaminated food.
  • Enterococcus – Found in feces, can cause urinary tract infections.
  • Acinetobacter – Opportunistic pathogen involved in hospital-acquired infections.

This diverse cocktail reflects organisms from skin, soil, water, and feces. Staphylococcus and Bacillus tend to be the most abundant due to human contact.

Do currency disinfection methods eliminate bacteria?

Research shows that commonly used disinfection techniques can significantly reduce bacteria on banknotes but may not completely eliminate all microbes.

Washing or wiping bills with antibacterial wipes, alcohol, or bleach solutions reduces contamination. However, certain resilient species can withstand brief surface disinfection.

Heating bills in microwaves or ovens substantially lowers bacteria counts and better targets internal contaminants but still may not achieve full sterilization.

More aggressive methods like autoclaving, UV light, ethylene gas treatment, and liquid disinfectant fully eradicate bacteria. But these require specialized equipment beyond typical consumer access.

While disinfecting paper money can provide some public hygiene benefit, risks from surface contamination are reasonably low compared to more direct transmission routes.

Potential viability of viruses on banknotes

In addition to bacteria, paper currency may also harbor viruses. These include:

Enveloped viruses

  • Influenza
  • Coronavirus
  • HIV
  • Herpes
  • Ebola

Enveloped viruses are potentially fragile outside hosts, so paper money contamination presents lower transmission risk. But some strains like influenza may persist for days, especially in dried mucus.

Non-enveloped viruses

  • Rhinovirus (common cold)
  • Rotavirus
  • Norovirus
  • Hepatitis A
  • Poliovirus

Hardier non-enveloped viruses survive longer on surfaces. Rhinovirus remains infectious for up to a week on banknotes ideal for hand-to-hand transfer.

However, prolonged viability declines at warmer temperatures. Virus survival also depends on material interaction, with polymers exhibiting antiviral properties.

Overall viral load on banknotes is generally low. But paper money serves as a proxy for hand contamination where self-inoculation of eyes, nose and mouth may occur after handling.

Can money transmit disease? Examples and risk assessment

Contaminated paper currency has been hypothetically implicated in the transmission of various infectious diseases. However, cash handling represents just one of many possible exposure routes. Specific evidence linking banknotes as a direct transmission vehicle in documented cases is lacking.

Methicillin-resistant Staphylococcus aureus (MRSA)

MRSA is sometimes detected on banknotes along with drug-resistant intestinal bacteria. This has raised concerns about currency spreading antibiotic resistance.

However, any purported connections between cash and MRSA infections are speculative. Paper money is unlikely to be a primary transmission pathway compared to close skin contact, crowded conditions, and poor hygiene.

At most, handling money may indirectly contribute to MRSA surface contamination that complements other exposure routes like skin-to-skin contact. But proximity and poor sanitary habits are larger factors.

Respiratory infections

Currency may harbor respiratory viruses like influenza, coronavirus, and rhinovirus that transfer via mucus or saliva. And viruses remain infectious longer on paper than hands.

But hands still play a greater role in self-inoculation of eyes, nose and mouth to initiate infection after handling money. Cash supports hand surface contamination rather than direct disease transmission.

The primary respiratory infection risks from paper money are likely from bringing contaminated hands in contact with facial mucous membranes, not directly from the banknotes.

Gastrointestinal infections

Potential enteric pathogens found on money include E. coli, Salmonella, and norovirus that cause gastrointestinal illnesses. Fecal-oral transmission could hypothetically occur from contaminated cash contact.

However, infectious oral doses require hundreds to millions of bacteria or virus particles, extremely unlikely from residual traces on bills. Like respiratory agents, currency likely only indirectly supplements other fecal-oral exposures rather than directly causing enteric disease.

Meticulous hand hygiene before eating and after money handling provides greater protection than cash disinfection or avoidance.

Blood-borne viruses

Theoretically, paper money could transmit blood-borne pathogens like HIV, hepatitis B, and hepatitis C between individuals through contaminated blood residues.

However, successful blood-borne transmission requires blood volumes measurable in milliliters rather than microscopic traces. Any blood on banknotes would dry within minutes, making transfer of an infectious viral dose improbable during typical cash transactions.

Direct blood exposures like needlestick injuries or transfusions pose the real risks for contracting blood-borne viruses rather than currency.

Safety tips for handling paper money

Cash will intrinsically harbor microbes, but potential risks during typical handling are minimal. Some reasonable precautions include:

  • Washing hands frequently when exchanging money to prevent indirect transfer from contaminated surfaces.
  • Avoiding touching eyes, nose or mouth after money handling until washing hands.
  • Not intentionally licking, chewing or swallowing banknotes to reduce oral contact with contaminants.
  • Being aware of overtly dirty, wet or visibly soiled currency and exchanging for cleaner bills when possible.
  • Using contactless payment methods like credit cards when available to avoid direct cash exchange.
  • Practicing general hygienic habits at all times.

For vulnerable groups at higher infection risk like infants, elderly and immunocompromised, extra care may be prudent with cash handling and hand hygiene.

Overall the risks are minor during typical banknote transactions and usage. Mere handling of paper currency itself does not pose inherent health hazards, and extreme avoidance is unnecessary in normal day-to-day usage.


Paper money does accumulate microbes from extensive handling, but risks of disease transmission are low. While currency can become soiled over time, the predominant bacteria and viruses are common species that briefly survive on dry surfaces compared to direct hand contact.

Disinfecting banknotes provides nominal additional safety beyond hand hygiene. Meticulous hand washing when handling cash, avoiding face contact and improving general hygiene offers greater health protection for the public than sanitizing money.

In essence, risks are ruled by proximity and exposure frequency. Cash supports hand surface contamination rather than direct infection, while hands facilitate self-inoculation of eyes, noses and mouths. Germs move from money to hands to mucous membranes, not directly from the currency.

Money itself is not dangerous, but serves as an intermediary in the multiple steps required for pathogens to ultimately cause infections. Awareness and prudent practices minimize any potential risks from cash handling. So by implementing sound hygienic habits, the public can rest assured that the cash in their pocket poses no unique hazard.