Drinking blood can absolutely make you sick, and it can do so in several distinct ways. The risks range from immediate nausea and vomiting to serious infections, iron poisoning, and even exposure to prion diseases. Whether the blood is human or animal, raw or partially processed, it carries hazards that the human body is not equipped to handle in any significant quantity. Some cultures have safely incorporated small amounts of cooked or fermented blood into their diets for centuries, but the key word is “small” and the key process is cooking.
Bloodborne Pathogens and Human Blood
The most alarming risk of drinking human blood is exposure to bloodborne infections. HIV, hepatitis B, and hepatitis C can all be present in infected blood, and the mouth provides a potential route of entry. Research on human bite injuries has established that oral mucosa exposed to another person’s blood creates a real transmission pathway for these pathogens.1PubMed Central. Human bites: bloodborne pathogen risk and postexposure follow-up algorithm Any cut, sore, or inflamed tissue in the mouth, gums, or throat gives viruses a direct route into the bloodstream. Even without visible wounds, the mucous membranes lining the mouth are far more permeable than intact skin.
You do not need to swallow a large amount. The concern is not really about what happens in the stomach, where acid would deactivate many pathogens, but about what happens on the way down. The soft tissue of the mouth, tongue, and esophagus can absorb viral particles before they ever reach stomach acid. This is why healthcare guidelines treat any oral exposure to blood as a potential infection event requiring testing and follow-up.
Zoonotic Risks from Animal Blood
Drinking raw animal blood carries a different but overlapping set of dangers. In parts of the world where raw blood consumption is a traditional practice, zoonotic diseases are a recognized concern. A study in the Konso district of Ethiopia, where a traditional dish called dhika sa’a is prepared from fresh, uncooked ruminant blood mixed with a local drink, found that while most residents were aware of at least one zoonotic disease, awareness of the full range of risks remained low.2MedCrave Online / MOJ Anatomy & Physiology. A habit of raw farm animal blood consumption and public awareness about associated health risks in konso district The diseases people named included tapeworm infection, anthrax, rabies, and tuberculosis, all of which can be transmitted from livestock to humans through contaminated tissues and fluids.
Raw cattle, goat, or sheep blood can harbor bacteria like Brucella, Salmonella, and E. coli, along with parasites such as Taenia (tapeworm). Some of these organisms survive well in fresh blood and can establish infection in the human gut. Tuberculosis, caused by Mycobacterium bovis in cattle, is another potential threat, though it requires the organism to be present in the animal at the time of slaughter. The bottom line is that raw animal blood is an unfiltered biological fluid from another species, and it comes with essentially the same food safety concerns as eating raw meat, except in liquid form that coats every surface of the mouth and throat.
Iron Overload
Blood is extraordinarily rich in iron. A single cup of whole blood contains roughly the amount of iron found in several days’ worth of food for an adult. Your body has no efficient mechanism for excreting excess iron once it has been absorbed. Small amounts are lost through skin shedding and minor bleeding, but if you take in more than you need, the surplus accumulates in organs like the liver, heart, and pancreas.
Occasional exposure to small quantities is unlikely to cause lasting harm, but repeated or large-volume consumption can push iron levels into dangerous territory. The condition that results, iron overload, causes fatigue, joint pain, abdominal discomfort, and over time can lead to liver cirrhosis, heart failure, and diabetes. This is the same process seen in hereditary hemochromatosis, a genetic condition where the body absorbs too much iron from ordinary food. Drinking blood simply accelerates the problem by delivering iron in a form, heme iron, that the gut absorbs very efficiently.
This iron problem is so central to blood as a food source that it has shaped the evolution of the few animals that actually live on blood. Research on vampire bats found that a gene called REP15 was lost during their evolutionary history, and this loss likely helped them adapt to extremely high dietary iron by enhancing iron excretion.3PubMed Central. Gene losses in the common vampire bat illuminate molecular adaptations to blood feeding Humans have no such adaptation. We are stuck with whatever iron we absorb, which makes blood a uniquely problematic substance for us to consume in quantity.
Protein Load and Kidney Stress
Blood is also a concentrated source of protein, primarily hemoglobin and albumin. Drinking blood delivers a protein hit that is far more concentrated than eating a steak. While healthy kidneys handle normal dietary protein without issue, very high protein loads from animal sources can cause the kidneys to work harder by increasing internal pressure and filtration rates.4PubMed Central. The Effects of High-Protein Diets on Kidney Health and Longevity Over time, this hyperfiltration can contribute to kidney damage, particularly in people who already have compromised kidney function.
In practice, the protein issue matters most for anyone consuming blood repeatedly rather than as a one-off. A single mouthful at a cultural ceremony is not going to damage your kidneys. But someone who adopted blood drinking as a regular habit would be subjecting their kidneys to a protein and waste-product burden that goes well beyond what a typical high-protein diet delivers. Blood also contains a significant amount of salt, which compounds the kidney workload.
The Prion Question
Prion diseases sit in their own category of risk because they are caused not by a living organism but by misfolded proteins that are almost impossible to destroy. Variant Creutzfeldt-Jakob disease, the human form of mad cow disease, has been shown to be transmissible through blood. Studies have demonstrated that infectivity exists in blood from animals and humans affected by bovine spongiform encephalopathy and vCJD, and human-to-human transmission has been documented through transfusions of red blood cells.5PubMed. The risk of transmitting prion disease by blood or plasma products
The prion risk from drinking blood is admittedly low in absolute terms. Prion diseases are rare, and the amount of misfolded protein in blood is far less than in brain or spinal tissue. But prions are not destroyed by cooking, stomach acid, or standard sterilization. Once ingested, they can cross the gut barrier and reach the brain, where they cause progressive, fatal neurodegeneration with no available treatment. Researchers are actively developing tests to screen blood donations for prion contamination, reflecting how seriously the medical community takes even the small risk of blood-borne prion transmission.6PubMed Central. Development of a sensitive real-time quaking-induced conversion (RT-QuIC) assay for application in prion-infected blood
This is the one risk that cooking does not address. Boiling, frying, or baking blood into food products eliminates bacteria and viruses, but prions survive temperatures that would sterilize virtually anything else. For this reason, blood sourced from cattle in regions with a history of BSE carries a theoretical prion risk regardless of preparation method.
When Cooking Changes Everything
Across many food traditions, blood is not consumed raw. Black pudding in Britain, blood sausage across continental Europe, sundae in Korea, and various blood soups and stews worldwide all involve thorough cooking. The safety profile of these foods is dramatically different from that of raw blood. A study on “Sanganel,” a traditional blood sausage from northeastern Italy, found that boiling the sausage for thirty minutes eliminated the bacterial population that would otherwise pose a food safety risk.7PubMed. Fate of the microbial population and the physico-chemical parameters of “Sanganel” a typical blood sausages of the Friuli, a north-east region of Italy
Heat kills bacteria, parasites, and viruses. A properly cooked blood sausage is no more dangerous, microbiologically speaking, than any other cooked meat product. The iron content remains high, but portions are small enough that a serving of black pudding delivers iron comparable to a serving of liver rather than the flood of iron you would get from drinking a glass of raw blood. These traditional preparations evolved alongside food safety intuitions: people figured out centuries ago that cooking blood made it safer, even without knowing the microbiology.
That said, the “cooked blood is safe” principle assumes the blood came from a healthy, inspected animal and was handled with the same hygiene standards applied to meat. Blood from a sick animal, or blood contaminated during slaughter, can harbor heat-resistant spore-forming bacteria like Clostridium that survive ordinary cooking. Food safety agencies in most countries regulate blood products used in food manufacturing for exactly this reason.
Cultural Blood Consumption in Practice
Several pastoral and semi-nomadic cultures have long traditions of consuming animal blood, and their experience offers a real-world test of the risks. The Maasai of East Africa have historically mixed cattle blood with milk as a food source, particularly during dry seasons and ceremonies. A dietary study of Maasai in one Kenyan region found that their daily diet was dominated by milk and ugali, a maize porridge, with fat intake high in saturated fatty acids and low in polyunsaturated fatty acids.8PubMed Central. High content of long-chain n-3 polyunsaturated fatty acids in red blood cells of Kenyan Maasai despite low dietary intake Blood was not a daily staple but an occasional supplement, and the quantities were modest compared to the volumes that would cause acute iron toxicity.
The distinction matters. Drinking a few tablespoons of blood mixed into milk during a ceremony is a very different exposure than drinking a full cup of raw blood on its own. Traditional practices tend to involve dilution, mixing with other foods, and infrequent consumption, all of which limit the dose of iron, protein, and any pathogens. When blood consumption has caused documented health problems in traditional settings, it has typically been linked to infected animals rather than to blood itself as a substance.
Nausea, Vomiting, and the Immediate Response
Even setting aside infection and toxicity, the human body tends to reject blood as a food. Drinking more than a small amount of fresh blood commonly triggers nausea and vomiting. Blood is thick, salty, and rich with iron, giving it a strong metallic taste that activates the gag reflex in most people. The stomach does not handle it smoothly either: the high protein content and iron can irritate the stomach lining, and the iron itself acts as an emetic at high doses.
Vomiting after drinking blood is arguably a protective response. By expelling the blood before it is fully absorbed, the body limits its exposure to pathogens and excess iron. People who have swallowed significant amounts of their own blood after a nosebleed or dental procedure often report nausea and dark, tarry stools afterward, which is the body processing the iron and protein it did absorb. The experience is unpleasant but generally not dangerous in those small quantities because it is the person’s own blood and therefore free of foreign pathogens.
Why Vampire Bats Can Survive on Blood Alone
The common vampire bat is one of only three mammal species that feed exclusively on blood, and its ability to do so required extensive evolutionary retooling. Genomic studies have identified dozens of gene losses in vampire bats that appear directly tied to the demands of a blood diet.3PubMed Central. Gene losses in the common vampire bat illuminate molecular adaptations to blood feeding Beyond the iron-excretion adaptation already mentioned, the loss of a gene called CYP39A1 may have contributed to enhanced cognitive abilities, possibly helping the bats track and return to feeding sources in complex social environments.
Vampire bats also depend on a specialized gut microbiome that helps them process blood. Research into the hologenomic adaptations of vampire bats has emphasized that understanding their diet requires looking at both the bat’s own genome and the microbial communities in its gut working together.9PubMed Central. Hologenomic adaptations underlying the evolution of sanguivory in the common vampire bat Their gut bacteria are tuned to extract nutrients from blood while managing the waste products that would overwhelm another mammal’s system.
A parallel example exists in the medicinal leech, another obligate blood feeder. Leeches maintain a highly simplified gut microbiome dominated by just two bacterial species that help them store and digest blood over extended periods.10PubMed Central. Culture-independent characterization of the digestive-tract microbiota of the medicinal leech reveals a tripartite symbiosis Earlier work had identified one of these, Aeromonas veronii, as an endosymbiont contributing to blood digestion.11PubMed Central. Symbiosis of Aeromonas veronii biovar sobria and Hirudo medicinalis, the medicinal leech: a novel model for digestive tract associations Humans have nothing like this microbial partnership. Our gut flora evolved to process a mixed diet of plants, fats, and cooked proteins, not raw blood.
The vampire bat comparison is useful because it highlights exactly what humans lack. These animals needed millions of years of genetic and microbial adaptation just to survive on blood. Every major challenge of a blood diet, iron overload, pathogen exposure, protein waste, nutritional deficiency in fats and carbohydrates, required a specific evolutionary solution. Humans have none of those solutions, which is why even modest blood consumption can cause problems that a vampire bat would never experience.
How Much Is Actually Dangerous
There is no precise threshold published in medical guidelines for “safe” blood consumption, largely because it is not a recognized dietary practice in the countries where most clinical research takes place. But rough estimates can be assembled from what we know about iron toxicity. Acute iron poisoning in adults typically begins at doses well above what normal food provides, and a single cup of whole blood delivers enough iron to approach that range for a small person. For most adults, a few tablespoons are unlikely to cause acute iron toxicity but may still trigger nausea and gastrointestinal distress.
The infection risk, however, does not follow a neat dose-response curve. A single drop of infected blood on a mouth ulcer can transmit hepatitis B, which is one of the most efficiently transmitted bloodborne viruses. For prion diseases, the infectious dose is unknown but believed to be very small. So while the toxicological risks of blood are somewhat dose-dependent, the infectious risks are better understood as binary: either the blood contains the pathogen or it does not, and if it does, even a small exposure can be enough.
For people who encounter blood in food traditions, the practical guidance is straightforward. Cooked blood products from inspected animals, eaten in normal portions, carry risks comparable to other organ meats. Raw blood from any source carries meaningfully higher risks, and raw human blood is the most dangerous category of all because it can carry pathogens specifically adapted to infect other humans.