Britannica Sources used in this answer

Where are new red blood cells made in the human body?

Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.

Blood plasma — blood Blood sediment in test tubes, showing plasma (clear fluid), red blood cells (red), and the release of hemoglobin into the surrounding plasma (pink).

In the human adult, new red blood cells are produced exclusively in the bone marrow. This process, known as blood cell formation, involves the differentiation of primitive stem cells into mature erythrocytes through several developmental stages.123

The rate of this production is regulated by erythropoietin, a hormone primarily produced in the kidneys, which signals the bone marrow to increase output when oxygen levels in the body are low.4

While the bone marrow is the sole site of red blood cell production in adults, the process shifts locations during development:
* Embryo: The yolk sac is the initial site of blood formation.1
* Fetal development: The liver becomes the primary organ for producing red blood cells before the bone marrow eventually takes over this role.12