Cryogenically frozen means preserved at extremely low temperatures, typically below minus 150 degrees Celsius (minus 238 degrees Fahrenheit). At these temperatures, biological activity essentially stops. Cells don’t divide, chemical reactions don’t occur, and decay halts entirely. The term gets used in two very different contexts: routine medical preservation of cells and tissues, and the more speculative practice of preserving entire human bodies after death in hopes of future revival.
What Counts as Cryogenic
The National Institute of Standards and Technology defines cryogenic temperatures as those cold enough to liquefy gases. Liquid nitrogen, the most common cooling agent in cryopreservation, boils at minus 195.8°C (minus 320.4°F). Liquid helium is even colder at minus 269°C (minus 452.1°F), though it’s rarely used for biological storage. In practice, most cryogenically frozen biological material sits in liquid nitrogen or its vapor phase, somewhere between minus 120°C and minus 196°C.
At these temperatures, time effectively pauses for biological material. A frozen embryo stored for ten years is biologically identical to one stored for ten days. That’s the core appeal of cryogenic freezing: it creates a kind of suspended animation where nothing degrades, at least in theory.
How Cells Survive Freezing
The biggest enemy of freezing isn’t the cold itself. It’s ice. When water inside a cell freezes, it forms sharp crystals that puncture cell membranes and destroy internal structures. To prevent this, scientists use chemicals called cryoprotectants that act like biological antifreeze. These substances (glycerol and DMSO are the most common) replace water molecules inside cells and prevent ice crystals from forming.
When cooling happens fast enough and cryoprotectant concentrations are high enough, the liquid inside cells transitions into a glass-like solid instead of crystallizing into ice. This process is called vitrification. Think of it as the difference between water freezing into jagged ice cubes versus hardening into smooth, clear glass. Vitrified tissue holds its structure far better than tissue that was simply frozen.
The catch is that cryoprotectants themselves are toxic to cells. Higher concentrations do a better job preventing ice, but they also damage cell membranes, impair enzyme function, unfold proteins, and can even harm DNA. At certain concentrations, DMSO thins cell membranes and eventually destroys their structure entirely. This toxicity problem remains the single greatest obstacle in cryopreservation, especially for larger, more complex tissues.
Medical Uses That Work Today
Cryogenic freezing is already a routine part of modern medicine, just at a small scale. Sperm, eggs, and embryos are cryopreserved by the millions every year for fertility treatment. Red blood cells are stored using 20 to 40 percent glycerol solutions. Stem cells for bone marrow transplants and CAR-T cells for cancer therapy are preserved in 5 to 10 percent DMSO before being thawed and infused into patients.
Frozen embryo transfer is now standard in IVF clinics worldwide. In one prospective study, frozen embryos produced live birth rates of about 9 percent per transfer cycle compared to 14 percent for fresh embryos. While that gap exists, frozen transfers are sometimes preferred because they give the body time to recover from the hormonal stimulation used to harvest eggs.
Whole organs are a different story. The current clinical standard for organ preservation is simple cold storage on ice, which keeps hearts viable for only 4 to 8 hours and kidneys for 24 to 36 hours. Researchers have recently achieved the first successful cryoprotectant-free preservation of a whole mammalian organ below zero degrees, and early work on “nano-warming” techniques (using tiny particles to rewarm vitrified tissue evenly) is showing promise for larger samples. But no one has yet frozen and successfully revived a full human organ for transplant.
Cryonics: Freezing Whole Bodies
When most people search for “cryogenically frozen,” they’re thinking about cryonics, the practice of preserving a legally dead person’s body at cryogenic temperatures. The idea is that future technology might one day be able to repair whatever killed the person, reverse aging, and restore them to life. It’s speculative, and no one has ever been revived from cryopreservation.
The process can only begin after a person is legally declared dead. Speed matters enormously, because cells begin deteriorating within minutes of death. Ideally, a standby team is present at the time of death to immediately begin cooling the body and circulating cryoprotectant solutions through the blood vessels. The goal is to vitrify the brain and body before ice crystals can form and destroy tissue structure.
Animal studies offer a glimpse of what’s possible and what isn’t. Researchers have perfused whole cat brains with 15 percent glycerol and frozen them, finding “almost normal cell arrangements” under microscopy after thawing. Rat brains perfused with vitrification solutions showed no visible ice formation, but neurons shrank significantly. Preserving structure at the microscopic level is one thing. Preserving it well enough to restore function is an entirely different challenge that no one has solved.
What It Costs
Two organizations dominate the cryonics industry. The Cryonics Institute in Michigan charges $28,000 for full-body preservation for lifetime members (who pay a one-time $1,250 membership fee) and $35,000 for annual members. Non-members or those whose arrangements are made after death pay $45,000. These fees cover the initial preservation and indefinite storage in liquid nitrogen. Alcor, based in Arizona, charges significantly more, particularly for its “neuro” option that preserves only the head.
Most members fund their preservation through life insurance policies, naming their cryonics organization as the beneficiary. Annual membership dues at the Cryonics Institute run $120 per year for those who don’t opt for lifetime membership.
The Legal Reality
Legally, a cryopreserved person is dead. They have no legal rights, no legal personhood, and their body occupies an unusual gray area in property law. In most jurisdictions, a dead body cannot be owned or bequeathed in a will. The next of kin typically holds a limited right to possess the body, but only for the purpose of disposal (burial, cremation, or in this case, cryopreservation).
This creates complications. If a cryonics organization goes bankrupt, or if family members disagree about what should happen to the preserved body, the legal framework for resolving those disputes is thin. Some legal scholars have argued that cryonics organizations could claim a property right over preserved remains, which raises concerns about exploitation of dying individuals and their families. The industry remains largely unregulated, operating in the space between funeral services and medical research without fitting neatly into either category.
Why Revival Remains So Difficult
Even under the best conditions, cryopreservation causes damage. Cryoprotectants toxic enough to prevent ice formation are also toxic enough to harm cell membranes, denature proteins, and cause structural changes in tissue. At high concentrations, DMSO binds to proteins and unfolds them. Some cryoprotectants are metabolized into compounds that cause acidosis or form crystite deposits in organs. And during cooling or warming, temperature differences across large tissues can cause fracturing, literal cracks in the preserved material.
For small, simple samples like individual cells or thin tissue slices, these problems are manageable. For a whole human brain containing roughly 86 billion neurons connected by trillions of synapses, the challenge is orders of magnitude greater. Every synapse would need to be preserved well enough to retain the information it encodes. Whether that’s even theoretically possible with current vitrification techniques is an open question. The people who choose cryonics are betting that future technology will be able to repair damage we can’t even fully characterize today.