Anemia can cause chills and cold intolerance directly, but fever is a less straightforward connection. Chills are one of the most recognized symptoms of iron-deficiency anemia, driven by poor circulation and reduced heat production. Fever, on the other hand, typically shows up only in specific types of severe anemia or when anemia leaves your immune system vulnerable to infections that then trigger the fever.
Why Anemia Causes Chills and Cold Intolerance
When you’re anemic, your blood carries less oxygen from your lungs to the rest of your body. That oxygen shortage disrupts two key processes your body relies on to stay warm: constricting blood vessels near your skin to conserve heat, and ramping up your metabolism to generate heat. With both of those responses impaired, you lose heat faster and produce less of it.
Iron deficiency makes this worse through a second pathway that has nothing to do with red blood cells. Your muscles need iron-containing enzymes to produce energy. When tissue iron is low, your muscles are less able to contract efficiently, which means even shivering (your body’s emergency heat generator) becomes less effective. The result is a persistent feeling of being cold, especially in your hands and feet, that doesn’t fully resolve by adding a sweater or turning up the thermostat.
This is why feeling constantly cold is one of the hallmark signs doctors look for. If you show up pale, exhausted, and complaining of chills, an iron check is often one of the first tests ordered.
When Anemia Actually Causes Fever
Most forms of mild to moderate anemia do not cause fever. But severe vitamin B12 deficiency is a notable exception. Between 28% and 60% of people with megaloblastic anemia (the type caused by B12 or folate deficiency) develop a low-grade fever. The proposed explanation is that the bone marrow goes into overdrive trying to compensate for the deficiency, and that hyperactivity generates enough metabolic heat to raise body temperature.
The fever in these cases is usually modest, staying at or below 101.3°F (38.5°C). It’s more likely to occur when the anemia is severe, particularly when red blood cells are abnormally large and other blood counts are also affected. Once B12 levels are restored, the fever resolves.
Hemolytic anemias, where red blood cells are destroyed faster than normal, can also produce fever. The rapid breakdown of red blood cells releases substances that trigger an inflammatory response, and fever is part of that cascade. One serious example is thrombotic thrombocytopenic purpura (TTP), a rare blood disorder where fever appears alongside anemia, low platelets, neurological symptoms, and kidney problems. This combination requires emergency treatment.
Fever From Infection, Not the Anemia Itself
The most common reason anemia and fever appear together is that the anemia has weakened your immune defenses, making you susceptible to infections that cause the fever. This is especially true for conditions that affect the bone marrow’s ability to produce white blood cells alongside red blood cells.
Aplastic anemia is a clear example. In this condition, the bone marrow fails to produce enough of any blood cell type. The resulting drop in white blood cells, particularly infection-fighting neutrophils, leaves you highly vulnerable to bacterial and fungal infections. Fever in someone with aplastic anemia is treated as a potential emergency because it often signals an active infection in a body with very limited ability to fight it off. In rare cases, aplastic anemia first reveals itself when someone shows up with a dangerous bloodstream infection.
Sickle cell anemia carries a similar risk. People with sickle cell disease have impaired spleen function, which means their ability to clear certain bacteria from the bloodstream is compromised. A fever in someone with sickle cell disease is always taken seriously for this reason.
Telling Chills Apart From Fever
It’s worth distinguishing between two experiences that can feel similar. Anemia-related chills are a sensation of being cold without an actual rise in body temperature. Your thermometer reads normal, but you feel like you can’t get warm. This happens because your body genuinely is producing and conserving less heat than it should.
Fever-related chills are different. When your body raises its internal temperature set point to fight an infection, you feel cold relative to that new, higher target. You shiver to generate heat, and your skin feels cold even as your core temperature climbs. If you’re anemic and experiencing shaking chills with a measurable fever, the fever is likely coming from an infection or an inflammatory process rather than the anemia alone.
Checking your temperature is the simplest way to sort this out. Persistent cold intolerance with a normal temperature points toward anemia as the direct cause. A reading above 100.4°F (38°C) suggests something else is going on, whether that’s a severe B12 deficiency, a hemolytic process, or an infection your anemia has made you more prone to.
Other Symptoms That Travel With Anemia
Chills and cold intolerance rarely show up in isolation. Most people with anemia significant enough to affect temperature regulation also experience fatigue, pallor (especially noticeable around the eyes and nail beds), shortness of breath with exertion, dizziness, and a faster-than-usual heart rate. Some people develop cravings for ice or non-food items like dirt or starch, a condition called pica that’s particularly associated with iron deficiency.
If fever is present alongside these symptoms, it adds urgency. The combination of anemia, fever, and unusual bruising or bleeding can indicate a bone marrow problem that needs prompt evaluation. Similarly, anemia with fever and dark or tea-colored urine may point to red blood cell destruction that requires immediate attention.
What’s Happening at the Blood Level
Anemia is defined by hemoglobin levels below specific thresholds. The WHO sets those at less than 12 g/dL for non-pregnant women and less than 11 g/dL for children under five and pregnant women. Men are generally considered anemic below 13 g/dL. The further your hemoglobin drops below these cutoffs, the more likely you are to experience temperature-related symptoms and, in severe cases, the fever associated with megaloblastic or hemolytic processes.
A complete blood count is the starting point for diagnosis, but when fever accompanies anemia, additional testing typically follows to identify whether an infection, B12 deficiency, or bone marrow problem is driving the fever. The treatment depends entirely on the underlying cause: iron supplements won’t resolve a fever caused by B12 deficiency, and B12 won’t help if the real problem is an infection exploiting a weakened immune system.