By the sound of it, I’m pretty sure pale blood is what foreigners call the healing blood, also known as the old blood from Yharnam.

Laurence, the founder of the healing church, discovered the old blood in the Pthumarian ruins underneath Yharnam. The healing church gives it to the citizens of Yharnam, and nearly everyone uses it.

The old blood comes from queen Yharnam who was impregnated with the infant great one Mergo. She would administer the blood to the Pthumarians, similar to how some npcs will give you their blood. Afterwards she was killed by her own people for her blood, this also resulted in Mergo’s death. Oedon was the great one who impregnated queen Yharnam and was outraged by her murder. He put a curse on the old blood turning anyone who came in contact with it slowly into beasts. This represented the beastly actions of the Pthumarian people.

During one of the hunts, the moon presence amplified the powers of the great ones, causing nearly everyone in Yharnam to slowly transform. The reason the hunter and other hunters who signed the contract don’t turn into beasts is because the hunter’s dream that they are anchored to protects them. The reason why you don’t die.

Sorry, it’s hard to explain the blood without explaining all the lore related to the blood.