Hematopoiesis is the blood cell production process. Cells that circulate in your blood include immune cells (white blood cells), red blood cells, and platelets. Your body produces an astonishing 100 billion blood cells each day. This is necessary because immune cells and red blood cells have short half-lives and, as the immune system’s foot soldiers, are often destroyed as they protect you from everyday invading pathogens.

In adults, hematopoiesis occurs in the bone marrow—the central cavity of your bones. Hematopoiesis starts with hematopoietic stem cells (HSCs), proliferative and multipotent cells that are located in specialized bone marrow regions called ‘niches’. HSCs can become any type of blood cell, a process that is tightly regulated by growth factors and other mediators. Through a series of steps that increase their commitment to becoming a specific cell type, HSCs ultimately give rise to the vast array of immune cells—monocytes, neutrophils, B cells, T cells, basophils, eosinophils—as well as platelets and red blood cells. These are then released into your blood stream. Hematopoiesis is a dynamic and highly tuned process that fluctuates to meet demand. For example, during infection your body needs more immune cells, so hematopoiesis escalates. However, unrestrained hematopoiesis can lead to immune cell over-supply that elevates inflammation and worsens disease. Many unhealthy lifestyle choices and habits, particularly regarding sleep, diet, and stress, can stimulate hematopoiesis and exacerbate immune and inflammatory diseases.