https://www.functionalps.com/blog/2012/09/26/ray-peat-phd-o…

https://www.functionalps.com/blog/2012/09/26/ray-peat-phd-on-carbon-dioxide-longevity-and-regeneration/
The regeneration of finger tips, including a well-formed nail if some of the base remained, will occur if the wounded end of the finger is kept enclosed, for example by putting a metal or plastic tube over the finger. The humidity keeps the wound from forming a dry scab, and the cells near the surface will consume oxygen and produce carbon dioxide, keeping the ratio of carbon dioxide to oxygen much higher than in normal uninjured tissue.
The amount of disorganized fibrous material formed in injured tissue is variable, and it depends on the state of the individual, and on the particular situation of the tissue. For example, the membranes lining the mouth, and the bones and bone marrow, and the thymus gland are able to regenerate without scarring. What they have in common with each other is a relatively high ratio of carbon dioxide to oxygen. Salamanders, which are able to regenerate legs, jaw, spinal cord, retina and parts of the brain (Winklemann & Winklemann, 1970), spend most of their time under cover in burrows, which besides preventing drying of their moist skin, keeps the ratio of carbon dioxide to oxygen fairly high.
“I think of high altitude as analogous to the protected gestational state. (Both progesterone and carbon dioxide are increased in people adapted to high altitude.) Respiratory acidosis, meaning the retention of carbon dioxide, is very protective, and is an outstanding feature of life in the uterus. Even at the time that an embryo is implanting in the uterus, adequate carbon dioxide is crucial. Many of the mysteries of embryology and developmental biology have been explained by the presence of a high level of carbon dioxide during gestation. For example, an injury to the fetus heals without scarring, that is, with complete regeneration instead of the formation of a sort of collagenous plug. Over the last fifty years, several people have discovered that simply enclosing a wound (for example an amputated finger tip) in an air-tight compartment allows remarkably complete regeneration, even in adults, who supposedly have lost the power of regeneration. (Exposure of tissues to air causes them to lose carbon dioxide.)”