If you’re someone interested in Cryogenically-freezing your body after death, you essentially believe that advances in science will eventually cure what killed you. Once cured, you’ll spring back to life and resume living free from illness.

According to a recent Popular Science article, the biggest hurdle facing cryonics goes above and beyond simply curing the cause of death. Instead, it’s more to do with reversing the damage incurred during the freezing process. Success in the field of cryonics will “depend on the quality of the cryopreservation as well as the quality of the revival technology,” according to Popular Science.

There’s a major difference between the preservation of organs during a prolonged cooling process versus cryogenic freezing an entire body for decades. We’ve all heard of the drowning victim who has been revived hours after being submerged in icy water. Cooling the body-in-this-case has a preserving effect similar to a heart being put on ice prior to a transplant. By no means is this similar to cryogenically freezing an entire body post mortem. Outside of a small selection of reptiles, amphibians, worms, and insects that seem impervious to being frozen during winter months, human tissue is significantly damaged during the freezing, then thawing process.

Cooling has a preservation effect, freezing, however, causes cell death. With ice formation rupturing cells and tissues, science must find a way to transition smoothly to a “glassy stage” (vitrification) avoiding the freezing stage altogether. According to Alexandra Stolzing’s Popular Science article, simple substances like sugars and starches have been known to protect cell membranes. “Chemicals like dimethyl sulfoxide (DMSO), ethylene glycol, glycerol, and propandiol are used to prevent intracellular ice formation and antifreeze proteins inhibit ice crystal growth and re-crystallizing during thawing.”

Since cooling doesn’t have the same detrimental effect on cell membranes as freezing does, cryogenic innovation relies on two things: improving preservation during freezing and advancing recovery after thawing. So far, cryopreservation breakthroughs have been isolated to simple human body parts like fingers and legs. In animals, however, scientists have cryopreserved, thawed, and successfully re-transplanted complex organs (kidney, liver, intestines), according to Popular Science. Whether it’s the wood frog (Rana Sylvatica) that freezes into an ice block during the winter months only to return back to life the following spring or the Nematode worm that remembers certain smells after its seasonal thaw, animals seem to have a better tolerance to being frozen.

Advances in human cell preservation have been seen mostly in healthcare. In the fertility sector, vitrified cells and simple tissues (eggs, sperm, bone marrow, stem cells, cornea, skin) are already being cryogenically frozen and transplanted. To reduce brain swelling during complicated deliveries, babies are being cooled right at the point of delivery. There’s even a cooling process after a cardiac arrest to reduce the body’s core temperature.

From patients with neuro-degenerative disorders requesting being frozen before death to terminal cancer patients hoping for revival after finding a cure, there are certainly some strong ethical and legal implications surrounding cryonics. Still, reviving whole bodies without compromising major organs is not possible with our current technology. The future of cryonics, according to Popular Science, relies heavily on nanotechnology. “Tiny, artificial molecular machines could one day repair all sorts of damage to our cells and tissues caused by cryonics extremely quickly, making revival possible.”