Cryogenically frozen means a body, tissue, or biological material has been cooled to extremely low temperatures, typically around -196°C (-320°F), to halt all biological activity. In everyday conversation, the phrase usually refers to cryonics: the practice of preserving a legally deceased person’s body in hopes that future technology can one day revive and heal them. But cryogenic freezing also has well-established, routine uses in medicine right now, from storing embryos for IVF to banking stem cells and blood products.
Cryogenics vs. Cryonics
These two terms get used interchangeably, but they refer to different things. Cryogenics is a branch of physics dealing with the production and effects of very low temperatures. It covers everything from superconducting magnets in MRI machines to rocket fuel. Cryonics is much narrower: it’s the specific practice of preserving human bodies (or heads) after legal death, with the goal of future revival. When most people ask “what is cryogenically frozen,” they’re thinking of cryonics, even if they don’t use that word.
How Cryopreservation Actually Works
The biggest enemy of freezing biological tissue isn’t the cold itself. It’s ice. When water inside and around cells freezes, it forms sharp crystals that puncture cell membranes and destroy tissue structure. To prevent this, cryopreservation relies on chemicals called cryoprotectants. These substances change how water molecules bond to each other, slowing their ability to cluster into ice crystals. As the concentration of cryoprotectant increases, the liquid becomes more viscous, and instead of freezing into ice, it transitions into a glass-like solid. This process is called vitrification.
Think of it like the difference between water turning to ice cubes (damaging) and honey slowly hardening in the cold (protective). In the vitrified state, molecules are essentially locked in place. There’s no molecular movement, no chemical reactions, no decay. A sample stored at liquid nitrogen temperature (-196°C) can theoretically remain stable for centuries.
Medical Uses That Already Work
Cryopreservation is routine in several areas of medicine. Fertility clinics freeze embryos, eggs, and sperm every day, and frozen embryos have produced healthy pregnancies after being stored for over 25 years. Blood banks cryopreserve rare blood types for transfusion. Bone marrow and stem cells are frozen and stored for transplant patients who need them weeks or months after collection. Researchers are also banking stem cells as a first step toward tissue engineering, with the long-term goal of growing replacement tissues for diseases that currently have no cure.
What these applications have in common is scale. Individual cells and small tissue samples freeze and thaw successfully because cryoprotectants can penetrate them evenly. The challenge grows enormously with size. A single embryo is a few cells. A human kidney has billions of cells arranged in complex structures with blood vessels that all need to be perfused with cryoprotectant at the right concentration, at the right speed. No one has yet successfully frozen and revived a whole human organ for transplant, let alone an entire body.
What Happens During Cryonic Preservation
Cryonics can only begin after a person is declared legally dead. This is a legal requirement, since the procedure has no medical recognition or regulatory approval. Ideally, the preservation team starts within one to two minutes of death to minimize damage from oxygen deprivation. The first step is restoring blood circulation and respiration artificially, not to bring the person back, but to keep cells supplied with oxygen while the body is rapidly cooled.
The blood is then gradually replaced with cryoprotectant solutions, similar to the antifreeze concept but with medical-grade chemicals designed to penetrate tissues. The goal is vitrification rather than straight freezing. Once the cryoprotectant has perfused the body, it is cooled over several days to -196°C and placed in a large insulated tank called a dewar, filled with liquid nitrogen. These tanks don’t require electricity. As long as the liquid nitrogen is topped off periodically, the temperature stays constant.
Some organizations offer “neuropreservation,” which preserves only the head and brain. The reasoning is that the brain stores a person’s identity, memories, and personality, and that any future technology capable of revival could presumably also regenerate or provide a new body.
How Well Does It Preserve the Brain?
This is the question that matters most for cryonics, and recent research is cautiously encouraging at small scales. High-pressure freezing of brain tissue, the gold standard in laboratory cryopreservation, can achieve what researchers describe as “pristine ultrastructural preservation.” In mouse brain samples, vitrification preserved membranes, organelles, synapses, myelin, and mitochondria with lifelike detail. In whole rat brains perfused with vitrification solution, researchers found no visible evidence of ice formation under microscopy, and synaptic structures remained well preserved, though neurons showed some shrinkage and fainter staining.
These results suggest that the connections between brain cells, widely believed to encode memory and personality, can survive the process. But there’s a significant gap between a rat brain perfused under ideal laboratory conditions and a human brain preserved after an unpredictable death, possibly with delays before the team arrives. The quality of preservation depends heavily on how quickly the process begins and how effectively the cryoprotectant reaches every region of the brain.
The Legal Status of Preserved People
Legally, a cryopreserved person is dead. Courts have consistently held that legal and medical definitions of death align: once brain-stem function has ceased, a person is dead for all legal and medical purposes. They are no longer a legal person, which creates complicated questions about their rights, their property, and who can make decisions about their remains.
Cryonics organizations see it differently. They refer to preserved individuals as “patients” rather than deceased, viewing the process as a medical intervention rather than a method of body disposal. This philosophical disagreement has real legal consequences. Disputes over whether someone should be cryopreserved often arise after the person has already died, meaning the individual who wanted the procedure can no longer advocate for themselves. Some legal scholars have argued that cryonic preservation could transform human remains into a form of property, a category that current law doesn’t neatly accommodate.
What It Costs
Whole-body cryopreservation typically costs around $200,000, roughly the price of a mid-range sports car, as one European cryonics company frames it. Neuropreservation (head only) costs less, though prices vary by organization. Most members fund the cost through life insurance policies, paying monthly premiums during their lifetime so the payout covers the procedure at death. One member of a European cryonics lab reported paying about $87 per month for combined membership and life insurance. Most clients at that facility are 60 or younger.
The fee covers not just the preservation itself but ongoing storage, which in principle must continue indefinitely. This raises questions about the financial stability of cryonics organizations over decades or centuries, a concern that has no easy answer.
The Case for Future Revival
Revival from cryopreservation is currently impossible. No human, no mammal, and no large organ has ever been frozen, stored, and successfully brought back to functioning life. Proponents argue this is a technology problem, not a physics problem, and that the information encoded in a well-preserved brain isn’t destroyed, just inaccessible with today’s tools.
The most detailed revival proposals rely on molecular nanotechnology: fleets of microscopic machines that could operate at extremely low temperatures, repair cellular damage molecule by molecule, replace damaged components, and gradually restore biological function. In theory, these nanodevices could clear cryoprotectant from the circulatory system, repair ice damage where vitrification was incomplete, fix pre-existing cellular problems like mutations or accumulated waste products, and even replace damaged structures inside cells. One proposed nanorobot design would enter each cell nucleus and swap out damaged chromosomes for corrected ones.
None of this technology exists yet. Molecular nanotechnology remains theoretical, and the engineering challenges are enormous. But cryonics advocates argue the bet is asymmetric: if the technology never arrives, you’ve lost nothing you wouldn’t have lost anyway. If it does arrive, and your brain was well preserved, you get a second chance. Whether that logic holds depends on how much confidence you place in technologies that may be decades or centuries away, and whether the organizations storing your body can survive that long.