Cryonics is the practice of preserving a human body at extremely low temperatures after legal death, based on the hope that future medical technology could one day revive and heal that person. It is not the same as cryogenics (the broader science of very cold temperatures) or cryopreservation used in fertility clinics, though it borrows techniques from both fields. Around the world, a few hundred people are currently stored in liquid nitrogen, and several thousand living members have signed up for preservation when they die.
How the Preservation Process Works
Cryonics procedures cannot legally begin until a person has been pronounced dead. But speed matters enormously, because cells begin deteriorating within minutes once blood stops flowing. Organizations like Alcor station “standby teams” near a dying member when possible. The moment death is pronounced, the team begins cardiopulmonary support using a mechanical chest compression device to keep oxygenated blood circulating. They pack the body in ice, administer anticoagulants to prevent clotting, and give a regimen of medications designed to slow the cellular damage that starts immediately after the heart stops.
Once the body is cooled to roughly 10°C, the next phase begins: replacing the blood with a cryoprotectant solution. These chemicals work like biological antifreeze, bonding with water molecules so they cannot organize into ice crystals. Ice is the enemy of cryonics because crystals shred cell membranes and destroy tissue structure. Traditional cryonics relied on glycerol, but modern protocols use more sophisticated mixtures containing compounds like ethylene glycol and propylene glycol. The goal is vitrification, which turns the body’s water into a glass-like solid rather than ice. Think of it as the difference between a window pane and a bag of crushed ice: one preserves what’s behind it, the other tears it apart.
After vitrification solution has been perfused through the vascular system, the body is slowly cooled further, past −120°C, and eventually placed into long-term storage in liquid nitrogen at approximately −196°C. At that temperature, all chemical reactions effectively stop. The body is stored in a large insulated vessel called a dewar, where it can theoretically remain indefinitely without further deterioration.
Whole Body vs. Brain Only
Cryonics organizations typically offer two options. Whole-body preservation does exactly what it sounds like. Neuropreservation preserves only the head, based on the reasoning that the brain contains a person’s identity, memories, and personality, and that any future technology capable of reviving someone could also reconstruct or provide a new body. Neuropreservation is significantly cheaper: Alcor, the largest U.S. provider, charges $80,000 for neuropreservation compared to a higher fee for whole-body preservation. Most members fund this through life insurance policies, paying small monthly premiums during their lifetime so the payout covers the preservation cost at death.
The Biggest Scientific Obstacles
No mammal has ever been revived after being cooled to cryogenic temperatures and stored. The Society for Cryobiology, the professional organization for scientists who study low-temperature biology, has stated plainly that “the knowledge necessary for the revival of live or dead whole mammals following cryopreservation does not currently exist.” They describe cryonics as “an act of speculation or hope, not science.”
The core problem is a catch-22 with cryoprotectants. You need high concentrations to prevent ice formation, but those same chemicals are toxic to cells. At the levels required for vitrification, cryoprotectants can breach cell membranes, damage DNA and proteins, impair enzyme function, and harm mitochondria, the structures that power cells. Researchers in the field have called cryoprotectant toxicity “the greatest obstacle to cryopreservation.” Reducing the concentration means risking ice crystals. Increasing it means poisoning the tissue you’re trying to save.
Rewarming presents its own challenge. Even if a body is perfectly vitrified on the way down, warming it back up unevenly can cause cracking and ice formation. Larger organs are especially vulnerable because the outside warms faster than the interior, creating thermal stress that can fracture the tissue like a glass dish pulled straight from a freezer into hot water.
Recent Progress in Organ Preservation
While reviving a whole human remains far beyond current capability, there have been genuine advances in preserving and rewarming individual organs. In 2023, researchers published results in Nature Communications showing they could vitrify rat kidneys, store them, rewarm them, and transplant them successfully into living rats. The key innovation was “nanowarming,” where iron oxide nanoparticles are distributed throughout the organ’s blood vessels along with the cryoprotectant solution. When placed in a radiofrequency coil, the nanoparticles generate heat from within, warming the entire organ simultaneously rather than just from the surface. This solves the cracking problem for small organs.
Separately, one company has cooled a pig kidney to −180°C without fracture using cold helium gas, and believes that applying pressure during cooling could allow dramatically faster cooling rates, reducing the time tissues are exposed to toxic cryoprotectants. These are promising steps for organ transplant medicine, but the gap between preserving a single rat kidney and preserving an entire human brain (with its roughly 86 billion neurons and trillions of connections) remains vast.
Legal Status of Preserved Individuals
Legally, cryopreserved individuals are dead. The process can only begin after a formal pronouncement of death, and courts in multiple jurisdictions have confirmed that legal death aligns with medical death, specifically the irreversible cessation of brain stem function. Cryonics organizations resist this framing. They refer to preserved individuals as “patients” rather than deceased, viewing the preservation as a pause rather than an endpoint. But in the eyes of the law, a cryopreserved person is no longer a legal person, which creates real complications.
Because the dead have no legal rights, disputes about what happens to a preserved body fall into murky territory. Family members have gone to court to prevent cryopreservation of relatives who wanted it, and legal scholars have argued that cryopreservation could transform human remains into property, since the body is being maintained rather than buried or cremated. Questions about who “owns” a preserved body, who can authorize its disposal, and what legal obligations a cryonics organization has to next of kin remain largely unresolved.
A Brief History
The first person ever cryopreserved was James Bedford, a psychology professor who died of kidney cancer on January 12, 1967, at age 73. His body was frozen within roughly two hours of death using a crude mixture of dimethyl sulfoxide and saline. Vitrification had not yet been developed, and the methods were primitive by today’s standards, making meaningful preservation of his brain tissue unlikely. Bedford’s body has been in continuous storage ever since, currently held at Alcor’s facility in Arizona. He left $100,000 to cryonics research in his will, though much of it was spent by his family defending his wishes in court against objections from other relatives.
What Cryonics Is Really Betting On
Cryonics is not based on any technology that exists today. It is a wager on two things: that the structure of the brain, even if damaged, retains enough information to reconstruct a person’s identity, and that some future technology (nanotechnology, advanced medicine, or something not yet imagined) will be able to repair the damage from both the original cause of death and the preservation process itself. Supporters argue that even a slim chance of revival is better than the certainty of cremation or burial. Critics counter that the chemical damage from cryoprotectant toxicity, combined with whatever ischemic damage occurred before preservation began, likely destroys the fine neural structures that encode memory and personality.
For now, cryonics exists in a space between science and faith. The underlying cryobiology is real, the preservation techniques are improving, and the recent success with rat kidneys shows the field is making measurable progress. But the leap from preserving a small organ to restoring a conscious human being is not incremental. It would require breakthroughs across multiple scientific disciplines that do not yet exist.