Elizabeth Báthory de Ecsed was a Hungarian noblewoman from the noble family of Báthory. According to the stories, she was apparently tortured some virgin and when the blood of one reached her skin by accident she realized that it appeared to be rejuvenating so the only logical step was to kill even more virgins to bath in their blood to stay young. This too isnt too farfetched.
https://en.wikipedia.org/wiki/Elizabeth_B%C3%A1thory
Also take a look what was a scientific experiment with the old mouse and positive effects from injection of young blood, drinking of young blood and bathing in young blood
https://www.scientificamerican.com/article/fountain-of-youth-young-blood-infusions-ldquo-rejuvenate-rdquo-old-mice/
The vampire stories about people drinking blood and not being able to step into the sun are not just a fairy tales
https://www.healthline.com/health/porphyria
https://en.wikipedia.org/wiki/Porphyria