The six most commonly recognized types of anemia are iron deficiency anemia, vitamin deficiency anemia, anemia of inflammation (also called anemia of chronic disease), aplastic anemia, hemolytic anemia, and sickle cell anemia. Each has a different cause, but they all share the same core problem: your blood can’t carry enough oxygen to meet your body’s needs. Anemia is formally defined as a hemoglobin level below 12.0 g/dL for women and below 13.0 g/dL for men.
Iron Deficiency Anemia
Iron deficiency anemia is the most common type worldwide. Your body needs iron to build hemoglobin, the protein inside red blood cells that carries oxygen. When iron runs low, your bone marrow produces fewer and smaller red blood cells, and each one carries less oxygen than it should.
The most frequent cause is blood loss. Heavy menstrual periods, bleeding ulcers, colon polyps, and regular use of pain relievers like ibuprofen or aspirin (which can cause slow bleeding in the digestive tract) all drain iron over time. Some people absorb iron poorly due to conditions like celiac disease, Crohn’s disease, or prior stomach surgery, including weight loss surgery. Endurance athletes can also lose iron through their digestive tract and through the physical breakdown of red blood cells during intense training.
Iron deficiency produces some distinctive physical signs beyond the usual fatigue and paleness. About 5% of people with iron deficiency develop spoon-shaped nails, where the nail plate becomes thin, brittle, and concave enough to hold a drop of water. Some people develop pica, an unusual craving to chew ice, dirt, or starch. These signs often appear before the anemia itself becomes severe, making them useful early warnings.
Vitamin Deficiency Anemia
When your body lacks vitamin B12 or folate, it can’t build red blood cells properly. The cells it does produce are oversized and underdeveloped, a condition called megaloblastic anemia. These larger-than-normal cells don’t function efficiently and die off faster than healthy ones.
The most common cause of B12 deficiency isn’t diet. It’s an autoimmune condition called pernicious anemia. Normally, your stomach produces a protein called intrinsic factor that binds to B12 so your gut can absorb it. In pernicious anemia, your immune system attacks the stomach cells that make intrinsic factor, effectively blocking B12 absorption no matter how much you eat. People following a strict vegan diet are also at risk, since B12 occurs naturally only in animal products. Certain medications, including acid-reducing drugs and some anti-seizure medications, can interfere with absorption of both B12 and folate.
Beyond the typical fatigue, B12 deficiency can cause tingling or numbness in the hands and feet, difficulty with balance, and cognitive problems like brain fog. These neurological symptoms can sometimes appear before the anemia shows up on blood tests.
Anemia of Inflammation
Chronic diseases like rheumatoid arthritis, kidney disease, cancer, heart failure, and even obesity can cause anemia through a less obvious route: inflammation. When your body is in a prolonged inflammatory state, it produces signaling molecules that trigger a cascade of changes in how iron is handled.
The key player is a hormone called hepcidin, produced by the liver. Inflammation, particularly through a signaling molecule called IL-6, ramps up hepcidin production. Hepcidin then blocks iron from entering the bloodstream by degrading the channels that move iron out of your gut lining, liver cells, and immune cells. The result is that you may have plenty of iron stored in your body, but it’s locked away where your bone marrow can’t use it. On top of that, inflammatory signals directly interfere with the production of red blood cells by suppressing the hormone that tells your bone marrow to make them.
This type of anemia is tricky because standard iron supplements often don’t help. The underlying condition driving the inflammation needs to be managed first.
Aplastic Anemia
Aplastic anemia is rare but serious. It occurs when bone marrow fails to produce enough blood cells of any kind, not just red blood cells. This means red blood cells, white blood cells, and platelets all drop simultaneously, a state called pancytopenia. That triple deficit creates a combination of fatigue (from low red cells), frequent infections (from low white cells), and easy bruising or bleeding (from low platelets).
In most cases, the immune system itself is the culprit. Certain immune cells become overactive and attack the stem cells in bone marrow that give rise to all blood cells. External triggers can also damage bone marrow directly, including chemotherapy drugs, industrial chemicals like benzene, radiation exposure, and certain viral infections such as Epstein-Barr virus. COVID-19 has also been linked to cases of aplastic anemia through similar immune disruption.
When a specific trigger like a drug or chemical exposure is identified, removing it sometimes allows marrow function to recover. In more severe cases, treatment may involve suppressing the immune system or replacing the damaged marrow entirely through a transplant.
Hemolytic Anemia
In hemolytic anemia, the body destroys red blood cells faster than it can replace them. Healthy red blood cells typically live about 120 days. In hemolytic anemia, that lifespan is cut dramatically short.
The causes fall into two categories. Intrinsic hemolytic anemias stem from defects within the red blood cells themselves, often inherited conditions that affect the cell’s membrane, internal enzymes, or hemoglobin structure. Extrinsic hemolytic anemias come from outside forces destroying otherwise normal red blood cells. These forces include autoimmune attacks (where the immune system mistakenly targets red blood cells), certain infections, mechanical damage from artificial heart valves, and reactions to medications or toxins.
When red blood cells break apart, they release their hemoglobin into the bloodstream. The body processes this free hemoglobin into bilirubin, a yellowish compound. If destruction outpaces the body’s ability to clear bilirubin, it builds up and can cause jaundice, a yellowing of the skin and eyes. The bone marrow tries to compensate by rapidly producing new red blood cells, which shows up on blood tests as an elevated reticulocyte (young red blood cell) count.
Sickle Cell Anemia
Sickle cell anemia is technically a type of hemolytic anemia, but it’s distinctive enough in its genetics, symptoms, and complications to be classified on its own. It’s caused by inheriting two copies of an abnormal hemoglobin gene, one from each parent. A single tiny change in the gene’s DNA swaps one amino acid for another in the hemoglobin protein, producing what’s called hemoglobin S instead of normal hemoglobin A.
People who inherit just one copy of the sickle gene (genotype AS) have sickle cell trait and typically experience few or no symptoms. Those who inherit two copies (genotype SS) have sickle cell disease. When oxygen levels in the blood drop, hemoglobin S causes red blood cells to deform from their normal flexible disc shape into a rigid crescent or sickle shape. These misshapen cells get stuck in small blood vessels, blocking blood flow and causing episodes of intense pain called vaso-occlusive crises. The sickled cells are also fragile and break apart easily, leading to chronic anemia.
Sickle cell anemia is most common in people of African, Mediterranean, Middle Eastern, and South Asian descent. It is identified through newborn screening programs in many countries, allowing early treatment that significantly improves outcomes.
How Symptoms Overlap and Differ
All six types share a core set of symptoms caused by reduced oxygen delivery: fatigue, weakness, pale or yellowish skin, shortness of breath during activity, dizziness, and cold hands and feet. These symptoms tend to develop gradually in chronic forms of anemia, which means many people adapt to them and don’t realize something is wrong until levels drop significantly.
What sets the types apart are their additional symptoms. Iron deficiency may bring spoon nails, pica, and a sore tongue. B12 deficiency adds neurological symptoms like numbness and cognitive changes. Aplastic anemia uniquely causes frequent infections and unusual bleeding or bruising because it affects all blood cell lines. Hemolytic anemias and sickle cell disease are more likely to cause jaundice and dark urine from the breakdown of red blood cells. Sickle cell anemia adds pain crises and, over time, organ damage from repeated blockages in blood vessels.
A standard blood test (complete blood count) is the starting point for diagnosis, but distinguishing between types requires additional tests. The size of red blood cells offers an important clue: iron deficiency produces small cells, vitamin deficiency produces unusually large cells, and other types may show normal-sized cells. From there, iron levels, vitamin levels, and more specialized tests help pinpoint which type is responsible.