Money is filthy. We’ve all heard that a hundred times. You touch a twenty-dollar bill and you’re basically shaking hands with everyone who bought a coffee or a bus pass in the last three years. But there is a darker, more literal side to this that forensic investigators and historians have to deal with constantly: blood on the money. It isn't just a plot point for a gritty noir film or a heavy metal album title. It is a genuine biological hazard and a complex forensic puzzle that changes how currency is handled, cleaned, and eventually destroyed by the Treasury.
Honestly, the reality of "dirty money" is way more clinical than the movies suggest. When physical cash gets caught in the crossfire of a violent crime, it stops being a medium of exchange and starts being a biohazard.
The forensic nightmare of stained currency
Biological fluid on a porous surface like a cotton-linen blend—which is what US banknotes actually are—presents a massive headache for crime lab technicians. Blood doesn’t just sit on top of the paper. It soaks into the fibers. This creates a permanent record of an event, but it also makes the bill incredibly difficult to process for DNA without destroying the integrity of the currency itself.
Forensic experts, like those who have worked with the FBI’s Laboratory Division, often have to prioritize. Do you want the DNA, or do you want the fingerprints? Usually, the blood provides a wealth of genetic information, but the chemicals used to "lift" prints, like ninhydrin, can sometimes interfere with the biological material. It's a trade-off.
You’ve probably seen shows where they spray luminol and everything glows neon blue. In real life, if there is blood on the money, that reaction is often messy because of the metallic inks and the various "background noise" of a bill that has been through thousands of hands. It isn't a clean glow. It's a smudge.
Why the Fed won't take your "red" cash
If you end up with a bill that has significant staining, don't expect the local vending machine to take it. Optical sensors in modern ATMs and change machines are calibrated to recognize very specific light-reflecting properties of the ink and the paper. Blood changes the light absorption. It looks like a "void" to the machine.
But it goes deeper than that.
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Banks have very strict protocols. If a teller sees what looks like significant biological contamination, they aren't supposed to just put it in the drawer. There is a specific "mutilated currency" protocol managed by the Bureau of Engraving and Printing (BEP). They handle the stuff that’s been through fires, floods, and yes, violent crimes.
Every year, the BEP’s Mutilated Currency Division in Washington, D.C., processes around 30,000 claims. They have people whose entire job is to sit with magnifying glasses and tweezers, reconstructing fragments of bills to prove their value. If there is blood on the money, it is often treated as a "contaminated" claim. This requires special handling because of pathogens like Hepatitis or HIV, which can actually survive in a dried state on surfaces for longer than most people realize.
The "Blood Money" term and its legal weight
We use the phrase "blood money" colloquially to mean profit from something unethical. However, in various legal systems and cultures, the concept is quite literal. In some Islamic jurisdictions, the practice of Diyya involves financial compensation paid to the family of a victim. This isn't just a "fine"—it is a recognized legal mechanism to prevent cycles of revenge.
But in the US legal system, the presence of blood on the money serves a more evidentiary purpose. It links a specific person to a specific location or act.
Think about the 1934 capture of Bonnie and Clyde. When the authorities searched the car, they found cash. Some of it was stained. That isn't just "loot" at that point; it's a physical link to the robberies and murders that preceded the shootout. It turns the currency into a witness.
Interestingly, money is surprisingly resilient. Most world currencies aren't actually paper. The US dollar is 75% cotton and 25% linen. Some countries, like Australia and Canada, use polymer (plastic). On polymer, blood wipes right off. It doesn't soak in. This makes it easier to clean, sure, but it also makes it harder for forensic teams to find evidence later. The "death of cash" and the rise of digital payments are slowly making the physical reality of blood-stained bills a relic of the past, but we aren't there yet.
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The biological lifespan of a stained bill
How long does the evidence last?
- Dried blood: Can remain detectable for decades if kept away from UV light.
- DNA stability: Forensic scientists have successfully extracted DNA profiles from currency used in crimes that occurred over 20 years ago.
- Microbial growth: If the money stays damp (say, buried in a backyard after a heist), the blood can act as a nutrient for mold, which eventually eats the cotton fibers, destroying the money entirely.
It is a race against time. The moment biological material hits a banknote, the clock starts ticking on the degradation of that evidence.
What you should actually do if you find stained currency
Let's say you're cleaning out an old house or you find a stash of cash that clearly has biological stains on it. Your first instinct might be to wash it.
Don't.
First off, if you suspect the blood on the money is linked to a crime, cleaning it is technically tampering with evidence. That's a felony you don't want. Secondly, household cleaners like bleach will destroy the security features of the bill. Bleach reacts with the starches (or lack thereof) in the paper and the "strip" inside, making the bill look like a counterfeit to any bank.
The correct move?
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- Bag it. Use a paper bag, not plastic. Plastic traps moisture and promotes mold growth which will rot the bill.
- Contact the BEP. They have a specific process for "Contaminated Currency" which includes currency that has been exposed to blood, body fluids, or sewage.
- Wait. The process can take months. They have to verify that at least 50% of the bill is present and that the stains don't prevent them from identifying the denomination and security markings.
The reality of "Dirty" money in circulation
A famous study often cited by news outlets claims that 90% of US bills have traces of cocaine on them. While that's a bit of an exaggeration (the "trace" amounts are often microscopic transfers from counting machines), the prevalence of biological material is real.
Researchers at NYU’s Dirty Money Project found that banknotes are a living ecosystem. They found thousands of types of bacteria, including those responsible for acne, gastric ulcers, and pneumonia. When you add blood on the money to that mix, you aren't just looking at a crime scene; you're looking at a public health variable.
But here’s the thing: money is treated with antimicrobial agents during the printing process. It isn't enough to kill everything, but it's why a bill doesn't just rot in your wallet. However, those agents are no match for a significant amount of blood.
Moving forward: The future of physical evidence
The shift toward digital currency is changing the landscape of "blood money." In 2026, we see fewer physical bank robberies and more ransomware attacks. You can't get blood on a Bitcoin.
Yet, as long as physical cash exists, the intersection of biology and economy will remain. It’s a grisly side of the financial world that most people never have to think about, but for the people in the basement of the BEP or the technicians in the state crime lab, it is just another Tuesday.
Actionable Insights for Handling Contaminated Currency:
- Avoid Physical Contact: If you encounter money with wet or dried blood, use gloves. Dried blood can still carry pathogens like Hepatitis B, which is notoriously hardy.
- Do Not Clean with Chemicals: Avoid using bleach, peroxide, or heavy detergents. These will strip the magnetic ink and holographic features, rendering the money worthless even if it’s legitimate.
- Use the Mutilated Currency Division: If the amount is significant (over $100), it is worth the effort to ship it to the Bureau of Engraving and Printing via registered mail. They are the only ones legally allowed to "exchange" such damaged currency for fresh notes.
- Documentation is Key: If the money was found in a suspicious context, take photos of it in situ before touching it. This preserves the "chain of custody" if a legal investigation follows.
Money is a tool, but it's also a physical object subject to the laws of biology. When those two worlds collide, the result is a complex, hazardous, and fascinating mess that requires expert handling to resolve.