What Is Bone Marrow? We Dig In on This Efficient Producer of Stem Cells

Answering the question "What is bone marrow?" should also involve an explanation of what it does and what can go wrong.

what s bone marrow

What is bone marrow? It's the spongy tissue inside some of the bones in the body, including the hip and thigh bones.

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What is bone marrow? It’s an efficient, blood cell-producing factory inside our bones. It has been described as soft, fatty, spongy, and gelatin-like. It’s heavy—about 5.7 pounds. Some bone marrow is red, some is yellow, and all of it is busy.

Our bone marrow produces stem cells that mature into red blood cells (200 billion every day), white blood cells (up to 100 billion), and platelets (400 billion). Below, we’ll delve into each, describing their role and what can go wrong, along with symptoms and treatment. (Also, click here to read our post When Do You Need a Bone Marrow Test?)

Red Blood Cells

Bone marrow produces stem cells that can become red blood cells, whose job is to distribute oxygen and carbon dioxide to the body’s cells, tissues, and organs. They have a life expectancy of between 100 and 120 days, and they become less active and more fragile with age. About 1 percent of the body’s red blood cells are removed every day by a type of white blood cell.

  • What can go wrong: Perhaps the most common red blood cell disorder is anemia, and there are five different types—iron deficiency, pernicious (B12 deficiency), aplastic (not enough red blood cells), autoimmune hemolytic (overactive immune system), and sickle cell anemia (red blood cells stick together).
  • Symptoms, plus examples of treatments (see chart): Fatigue, weakness, pale or yellowish skin, shortness of breath, dizziness, irregular heartbeat, chest pain, headache, cold hands/feet.
    Condition Treatment
    Iron deficiency Iron supplements
    Pernicious anemia High-dose B12 supplements
    Aplastic anemia Transfusions, bone marrow transplant
    Autoimmune hemolytic anemia Immune suppressants (e.g., prednisone)
    Sickle cell anemia Blood transfusions, pain meds, bone marrow transplant

White Blood Cells

Five different kinds of white blood cells are produced by bone marrow to fight infections and outside forces like smoke and dust. When you have an infection, the number of white blood cells increases significantly. White blood cells make up only 1 percent of our blood, and a drop of blood contains between 7,000 and 25,000 white blood cells. Think of them as your bodyguards who have a lifespan of only one to three days.

  • What can go wrong: Although it can start in other types of blood cells, leukemia is a cancer in which the cells are abnormal. They don’t die when they should, and they may crowd normal white cells out. Two forms of leukemia are acute; four are chronic. The ones more common in older adults are acute myeloid leukemia, chronic lymphoid leukemia, and chronic myelomonocytic leukemia.
  • Symptoms, plus examples of treatments (see chart): Fever, chills, fatigue, infections, lost weight, swollen lymph nodes, bleeding/bruising, nosebleeds, bone pain/tenderness.
    Condition Treatment
    Acute myeloid leukemia Chemotherapy, targeted drug therapy, stem cell transplant
    Chronic lymphoid leukemia Chemotherapy, rituximab, bendamustine, ibrutinib, alemtuzumab with rituximab
    Chronic myelomonocyctic leukemia Azacytidine, decitabine, hydroxyurea, stem cell transplant, transfusions, antibiotics


We need platelets to help blood clot and stop bleeding. A normal platelet count is 150,000 to 450,000 per microliter of blood. The risk for spontaneous bleeding develops if a platelet count falls below 10,000 to 20,000. Each platelet has a lifespan of seven days. When a blood vessel is damaged, it sends a message that is picked up by platelets, which rush to the affected area and repair it.

  • What can go wrong: The answer here may be not enough platelets, too many platelets, or platelets that don’t clot as they should. In a condition called thrombocytopenia, the bone marrow makes too few platelets. It can be caused by certain medications, cancer, kidney disease, pregnancy, infections, and a malfunctioning immune system. When bone marrow produces too many platelets, it’s called thrombocythemia. It can result in blood clots that block the flow of blood to the brain or heart. The cause is unknown.Thrombocytosis is also caused by too many platelets, but the count is not as high as in thrombocytopenia. It’s caused by another disease or condition that stimulates the bone marrow to make more platelets.

    In some cases, the problem is simply platelet dysfunction. It is caused by diseases (kidney disease, Lupus, multiple myeloma), infection, or certain drugs (aspirin, NSAIDS, other antiplatelet medications).

  • Symptoms, plus example of treatments (see chart): Easy bruising, hard-to-stop bleeding, blood in stools/urine, fatigue, heavy menstrual flows, yellowish skin.
    Condition Treatment
    Thrombocytopenia Change in medications, blood/platelet transfusions, corticosteroids, splenectomy
    Thrombocythemia Observation, hydroxyurea, anagrelide, interferon
    Thrombocytosis Low-dose aspirin, hydroxyurea, anagrelide, interferon, plateletpherisis

Other Cancers That Affect Bone Marrow

Multiple myeloma occurs in plasma cells that originate in bone marrow. They make antibodies that guard against bacteria. People who have multiple myeloma have plasma cells that don’t reproduce normally. Instead, they become cancerous, divide, and grow out of control, often appearing in several places in the body. The cause is unknown. Bone damage is the primary effect of the disease.

Multiple myeloma is treated by chemotherapy, stem cell transplant, radiation, and surgery.


A bone marrow transplant, also called a stem cell transplant, might be used to treat diseases such as leukemia, anemia, multiple myeloma, lymphoma, and immune deficiencies. It can come from the patient or from a donor. It can replace diseased bone marrow or help re-start the immune system, and it can come from bone marrow, blood vessels, and umbilical cord blood collected after birth.

Although life-saving and safe for some, bone marrow transplants carry serious and perhaps fatal risks for others.

Lymphomas are cancer cells in the lymphatic system that can develop in multiple locations, including in bone marrow. You’ll recognize them by their names—non-Hodgkin lymphoma and Hodgkin lymphoma. Both affect white blood cells, the only difference being a specific type of cell present in Hodgkin’s lymphoma.

Lymphomas are not preventable, but survival rates with treatment are good. It includes biologic therapy (drugs that trigger the immune system to attack cancer cells), antibody therapy (to counteract antigens), chemotherapy and radiation (to kill cells), steroids, and surgery.

Bone Marrow: Life-Giving, But Vulnerable

Bone marrow is life-giving and essential, but also vulnerable and at times malfunctioning. Getting regularly scheduled physical exams that include blood tests is the best way to guard against and get early treatment for bone marrow disorders.

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Jim Brown, PhD

As a former college professor of health education, Jim Brown brings a unique perspective to health and medical writing. He has authored 14 books on health, medicine, fitness, and sports. … Read More

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