Parabiosis experiments, surgically joining the circulatory systems of a young and an old animal, produced one of the more striking findings in aging biology: aged tissue in the older animal showed measurable rejuvenation effects, and young tissue in the younger animal showed some accelerated aging effects, suggesting blood carries both rejuvenating and aging-promoting factors. That result is well replicated in animal research and forms a legitimate branch of aging science, with ongoing work trying to identify exactly which blood factors drive the effect.
What has NOT been established is that infusing whole young-donor plasma into humans reproduces this effect safely or meaningfully. Isolating and testing the specific responsible factors is a very different, much harder scientific task than the original whole-blood parabiosis experiments, and that gap has been exploited commercially: clinics offering young-donor plasma infusions marketed as anti-aging treatments have drawn explicit public warnings from health regulators about lack of proven benefit and real safety risk.
This entry is included specifically to separate two things this site treats very differently: the genuine, ongoing research into blood-borne aging factors (Conboy and Wyss-Coray's labs are central to this work) versus the commercial plasma-infusion offerings built on top of that research's early promise. Readers encountering plasma-therapy marketing should understand which of the two they're looking at.