The most widely used substance for preserving human bodies today is formaldehyde, typically in a water-based solution called formalin. It works by chemically cross-linking proteins so that bacteria cannot break tissue down. But formaldehyde is only one chapter in a long story: humans have been preserving their dead for thousands of years using plant resins, oils, waxes, and even extreme cold. The methods vary dramatically depending on whether the goal is a funeral viewing, medical education, museum display, or something more speculative like cryonic suspension.
How Formaldehyde Actually Works
Formaldehyde is a simple organic molecule, just one carbon atom bonded to hydrogen and oxygen. When dissolved in water at concentrations around 37 percent, it becomes formalin, the standard preservative in funeral homes and anatomy labs worldwide. Once injected into the body’s arterial system, formaldehyde reacts with tissue proteins by inserting small chemical bridges between adjacent protein molecules, effectively locking them into place. About four to five grams of formaldehyde are needed to fully fix 100 grams of soluble protein, and insoluble proteins require even more.1PubMed Central. Human body preservation – old and new techniques – Section: Preservatives or fixatives This cross-linking is what gives embalmed tissue its characteristic firmness. It also reacts with lipids, though less efficiently, by targeting unsaturated bonds in fats.
In a typical funeral embalming, the embalmer makes a small incision near the collarbone or inner thigh, locates an artery, and uses a pump to push embalming fluid through the circulatory system while draining blood from a nearby vein. The embalming fluid is not pure formalin; it usually contains dyes to restore a lifelike skin tone, humectants to prevent tissue from drying out too quickly, and surfactants to help the fluid penetrate evenly. The internal organs, especially the abdominal and thoracic cavities, are treated separately with a stronger solution using a long needle called a trocar. The entire process takes a few hours and is designed to keep the body presentable for a viewing period of several days to a couple of weeks.
What the Ancient Egyptians Used
Long before formaldehyde existed, ancient Egyptians developed remarkably sophisticated preservation techniques. Their embalming materials were not simple herbs sprinkled over a body; they were carefully formulated mixtures of oils, resins, and waxes, many sourced through long-distance trade networks. A 2023 analysis of mummification balms from the Valley of the Kings identified ingredients including beeswax, plant oils, animal fats, bitumen, pine-family resins, balsamic substances, and resins from dammar or pistachio trees.2PubMed Central. Biomolecular characterization of 3500-year-old ancient Egyptian mummification balms from the Valley of the Kings These ingredients were not chosen at random. Pine resins and balsamic substances have natural antibacterial properties, bitumen creates a water-resistant seal, and beeswax helps bind everything together.
A separate study of embalming residues from the Saqqara burial complex used chemical analysis to identify specific mixtures of antiseptic oils, tars, and resins applied to the head and wrappings. The researchers were also able to decode terms that appear in ancient Egyptian texts: “antiu,” usually translated as “myrrh” or “incense,” turned out to refer to a mixture based on coniferous oils or tars, and “sefet,” described as “a sacred oil,” was actually an unguent blended with plant additives.3PubMed Central. Biomolecular analyses enable new insights into ancient Egyptian embalming In other words, even the Egyptians’ own labels did not fully capture the complexity of what was in the jar.
The embalming process itself involved removing the brain (usually through the nose) and the abdominal organs, drying the body with natron (a naturally occurring salt), and then treating it with these resinous balms before wrapping it in linen. The combination of desiccation and antimicrobial resins could preserve soft tissue for millennia.
Renaissance Experiments and the Road to Modern Embalming
Between ancient Egypt and the modern funeral home lies a long period of experimentation. During the Renaissance, as medical schools needed cadavers for dissection, preservation became a practical necessity rather than a purely ritual one. Early approaches included injecting colored solutions into blood vessels to map the circulatory system. Alessandro Giliani, who died in 1326, used arterial injections of colored solutions that hardened in place. Leonardo da Vinci developed his own embalming fluids from mixtures of turpentine, camphor, lavender oil, wine, rosin, and potassium and sodium nitrate. Other anatomists tried simpler approaches: Jacobus Berengar injected warm water into veins, while Bartholomeo Eustachius reportedly used injections of warm ink.4PubMed Central. Human body preservation – old and new techniques – Section: Period of anatomists
None of these methods preserved tissue the way formaldehyde would later do. They were designed to keep a body usable for a few weeks of study, not to halt decomposition indefinitely. Formaldehyde emerged as the dominant embalming chemical in the late 1800s and has held that position ever since, largely because nothing else is as cheap, effective, and widely available for the purpose.
The Health Risks of Working with Formaldehyde
For all its effectiveness, formaldehyde is toxic. Even at low concentrations of 0.1 to 2.7 parts per million in the air, it irritates the eyes, nose, and throat. Higher exposures can cause lung damage and allergic sensitization. The International Agency for Research on Cancer classifies formaldehyde as a human carcinogen, and no safe exposure threshold has been established.5International Journal of Ayurveda Orientation. Formalin Exposure in Anatomy Laboratories: Health Risks and Integrated Strategies
The people most at risk are those who work with formaldehyde regularly: embalmers, anatomy lab technicians, and pathologists. A large study of funeral industry workers found that long durations of formaldehyde exposure from embalming were linked to a higher risk of death from myeloid leukemia.6Journal of the National Cancer Institute. Funeral Industry Workers Exposed to Formaldehyde Face Higher Risk of Leukemia The dose-response relationship was clear: workers who had performed embalming for more than 34 years, or who had completed more than about 3,000 lifetime embalmings, had roughly three to four times the risk of myeloid leukemia compared to those with fewer embalmings. Peak formaldehyde exposure levels mattered as well. These increased risks did not extend to other blood cancers or brain cancer.7PubMed Central. Mortality From Lymphohematopoietic Malignancies and Brain Cancer Among Embalmers Exposed to Formaldehyde
For anatomy students and medical professionals who spend time in dissection labs, the exposures are lower but still concerning. Symptoms like headaches, watery eyes, and chronic nasal irritation are common complaints. Many anatomy departments have responded by improving ventilation, using downdraft dissection tables, and exploring alternative preservation methods.
Formaldehyde in the Ground
Once an embalmed body is buried, the formaldehyde in its tissues does not simply vanish. Environmental scientists have investigated whether embalming chemicals can leach out of cemeteries and contaminate surrounding soil and groundwater. A study of cemetery soil in Middle Tennessee found that most samples showed no detectable formaldehyde, except for one from a 1952 burial site, which had measurable levels. The researchers concluded there was a low likelihood of contamination reaching waterways or affecting nearby residents.8PubMed Central. The Impact on Environmental Health from Cemetery Waste in Middle Tennessee A study of cemetery leachate in Nigeria detected formaldehyde, ethanol, and other organic compounds in cemetery-adjacent soil and groundwater samples, though some readings fell below detection limits.9Journal of Chemical Society of Nigeria. ESTIMATION OF EMBALMING CONTAMINANTS IN SOIL AND GROUNDWATER SAMPLES FROM CEMETERY LEACHATES IN MBAIORBO, MBADIM-MBATIAV LEACHFIELD IN GBOKO, NIGERIA
The picture that emerges is mixed. Formaldehyde breaks down in soil over time through natural microbial action and chemical reactions, so it does not accumulate the way heavy metals might. But burial density matters. A city cemetery used continuously for over a century, sitting above a shallow water table, poses a different risk profile than a rural cemetery with widely spaced graves. This concern is one of several factors driving interest in “green burial” practices that skip embalming entirely.
Thiel Embalming and the Push for Softer Alternatives
In medical education, the stiff, discolored cadavers produced by traditional formalin fixation have long been a frustration. Formalin hardens tissues, changes their color, and fills labs with irritating fumes, all of which compromise the training experience for surgical residents who need to practice on tissue that behaves like living flesh.10PubMed Central. Preparation of Soft Embalmed Cadavers by the Modified Thiel Embalming Technique for Surgical Skill Training and Development of a Universal Quantitative Scoring System to Assess the Suitability of Soft Embalmed Cadavers for Such Training Purposes
Thiel embalming, developed by Walter Thiel in the 1990s, addresses these problems. It uses a cocktail of chemicals including salts, boric acid, ethylene glycol, and only very small amounts of formalin, resulting in cadavers that retain natural color, flexibility, and tissue feel. Surgeons can practice cutting, suturing, and moving joints in ways that are impossible with traditionally preserved bodies.11PubMed Central. Thiel’s embalming method with additional intra-cerebral ventricular formalin injection (TEIF) for cadaver training of head and brain surgery The downside is cost and complexity: Thiel embalming requires more chemicals, a longer immersion period (often weeks to months), and careful temperature control. Modified versions of the technique have emerged, tweaking the recipe to suit local needs and budgets, and researchers have developed scoring systems to assess how well the preserved tissue mimics living tissue for surgical training.
Thiel-embalmed cadavers are now widely used for surgical workshops around the world, particularly for specialties like neurosurgery, orthopedics, and head-and-neck procedures where realistic tissue handling is critical. For general anatomy teaching, though, the higher cost still limits adoption, and many schools continue to rely on traditional formalin fixation with improved ventilation.
Refrigeration and Its Limits
Not every form of body preservation involves chemicals. Refrigeration is the simplest and most immediate method used in morgues, hospitals, and funeral homes to slow decomposition between death and final disposition. Standard morgue refrigerators hold bodies at around 2 to 4 degrees Celsius. At those temperatures, bacterial activity slows dramatically but does not stop entirely, so refrigeration is a short-term measure, effective for days to a few weeks depending on the condition of the body at intake.
Refrigeration is routinely used before autopsy, but researchers have pointed out that its effects on decomposition timing are not as well understood as you might expect. One study noted that the impact of body refrigeration on estimating time since death using standard scoring methods and insect-based analysis remains insufficiently studied.12PubMed. The impact of body refrigeration on decomposition and postmortem interval estimation This matters in forensic contexts where accurately estimating the postmortem interval is important for criminal investigations. A body that has been refrigerated for several days before being found outdoors can throw off decomposition-based timelines.
Plastination for Permanent Display
If you have ever visited a Body Worlds exhibition and wondered how those preserved human specimens maintain their shape without any visible fluid or container, the answer is plastination. Developed by anatomist Gunther von Hagens in the late 1970s, the technique replaces all water and fat in biological tissue with a curable polymer, typically silicone. The result is a dry, odorless specimen that can be touched, posed, and displayed at room temperature indefinitely.
The process involves several stages. First, the tissue is fixed, usually with formalin. Then the water is replaced with acetone through a series of baths. The critical step is called forced impregnation: the specimen is submerged in liquid silicone inside a vacuum chamber. As the pressure drops, acetone boils out of the tissue at low temperature and silicone is drawn in to replace it. Because the silicone mixture is too thick to passively diffuse into the tissue, the vacuum provides the necessary driving force.13The Journal of Plastination. Silicone Plastination of Biological Tissue: Cold-temperature Technique Biodur© S10/S15 Technique and Products – Section: Materials and Methods Once the silicone has fully replaced the acetone, the specimen is cured with gas, and it hardens permanently.
One of the challenges with plastination is tissue shrinkage. A study comparing two different silicone products for plastination found that the choice of polymer affected how much the tissue contracted during forced impregnation, which matters when accurate anatomy is the goal.14PubMed Central. Plastination with low viscosity silicone: strategy for less tissue shrinkage Despite this limitation, plastinated specimens are now found in medical schools and public exhibitions worldwide. They are especially useful for teaching anatomy in settings where maintaining preserved cadavers in fluid-filled tanks is impractical.
Cryonics and Vitrification
At the speculative end of preservation science sits cryonics: the practice of cooling a legally deceased person to extremely low temperatures in the hope that future technology might be able to revive them or repair whatever caused death. Cryonics is not mainstream science, and no one has ever been revived from cryopreservation. But the underlying chemistry of how bodies are prepared for long-term cold storage is genuinely interesting.
The core problem cryonics tries to solve is ice crystal formation. When tissue freezes slowly, water inside cells forms large ice crystals that puncture cell membranes and destroy structures. To counter this, cryonics organizations use vitrification: a process that replaces bodily fluids with high concentrations of cryoprotective agents, essentially a kind of biological antifreeze, and then cools the body rapidly enough that the fluid solidifies into a glass-like state without crystallizing. Permeable cryoprotectants enter cells directly, while nonpermeable ones work outside cells to draw water out and prevent ice nucleation.15Theoretical and Natural Science. Technical examination of cryonics
The catch is that the cryoprotective agents themselves are toxic at the concentrations needed for vitrification. Finding a balance between preventing ice damage and causing chemical damage remains one of the central unsolved problems in cryobiology. Bodies stored by cryonics organizations are kept in liquid nitrogen at roughly minus 196 degrees Celsius, a temperature at which essentially all chemical reactions stop. Whether the preservation is good enough to allow future repair is a question that no current science can answer.
When Nature Does the Preserving
Some of the best-preserved ancient human remains were never embalmed at all. Extreme cold, acidic bogs, and arid deserts can all halt decomposition naturally under the right conditions.
The frozen mummies of the Andes are a striking example. High-altitude Inca sacrificial sites at elevations above 5,000 meters have yielded remarkably intact human remains, preserved by the constant sub-zero temperatures of mountain peaks. Mummies recovered from mounts like Llullaillaco (6,739 meters) and Aconcagua have been studied with CT scans and X-rays, revealing preserved internal organs, intact skin, and even identifiable stomach contents. These individuals were not embalmed; the extreme cold did the work, essentially freeze-drying the bodies over centuries.16PubMed Central. Frozen Mummies from Andean Mountaintop Shrines: Bioarchaeology and Ethnohistory of Inca Human Sacrifice
Bog bodies, found in peat bogs across Northern Europe, are preserved through a different mechanism. The highly acidic, oxygen-poor water of sphagnum peat bogs inhibits bacterial growth and tans skin and soft tissue in a process loosely similar to leather tanning. Bodies thousands of years old have been pulled from bogs with recognizable facial features, fingerprints, and even stomach contents intact, though their bones often dissolve in the acidic water. Desert mummies, meanwhile, owe their preservation to rapid desiccation: in dry heat, a body can lose moisture faster than bacteria can break it down, leaving behind dried but structurally intact tissue.
These natural processes share something in common with intentional preservation methods: they all work by making the body inhospitable to the microorganisms that cause decay. Whether that happens through chemical fixation, extreme cold, acidity, or simple dryness, the underlying principle is the same. The difference is control. Modern techniques let you choose how the body will look, how long it will last, and what it can be used for. Nature just takes whatever conditions are available and, occasionally, produces something that outlasts all human efforts.