Red blood cells carry oxygen from the lungs around the body. They then carry carbon dioxide from around the body back to the lungs.

These cells are an important component of blood. However, a range of conditions can cause problems with how red blood cells work or how many are in the bloodstream.

This article explores what red blood cells are in more detail. It also lists some disorders that affect them, discusses red blood cell counts, and answers some common questions.

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Red blood cells, also called erythrocytes, begin as immature cells in the bone marrow. After about 7 days of maturation, they make their way into the bloodstream. Each red blood cell lives for roughly 120 days.

They are red in color and shaped like a disk, with a flat center that causes a slight indentation in the middle. They are the most abundant type of cell in the blood.

Red blood cells have no nucleus and can easily change shape. This helps them fit through various blood vessels throughout the body.

What do they do?

These cells contain a protein that healthcare professionals call hemoglobin, which helps them carry oxygen around the body.

After a person breathes in oxygen using their lungs, the red blood cells collect this oxygen from the lungs and carry it through the bloodstream to different cells around the body.

The red blood cells also collect carbon dioxide from the body’s cells and carry it back to the lungs. A person then exhales this carbon dioxide.

This section explores a variety of red blood cell disorders.


Anemia is a condition that occurs when the number of red blood cells in a person’s bloodstream, or the hemoglobin concentration within these cells, is lower than usual.

If a person has anemia, their red blood cells have a decreased ability to carry oxygen to the body’s cells via the bloodstream.

This may cause the following symptoms:

If a person develops severe anemia, they may experience:

Sickle cell disease

Sickle cell disease (SCD) is a group of disorders that affect a person’s red blood cells from birth.

With SCD, an issue with hemoglobin causes the red blood cells to become hard and sticky. It also causes the cells to become C-shaped, similar to a farm tool called a sickle.

Sickle-shaped cells die early, causing a person to have a continual shortage of red blood cells. The cells can also become stuck in blood vessels, which can disrupt the flow of blood.

Common symptoms of SCD include:

  • extreme fatigue due to anemia
  • jaundice, which refers to a yellowing of the skin and the whites of the eyes
  • dactylitis, which refers to painful swelling of the hands and feet

Seeking medical help

SCD can lead to serious health problems that may be life threatening.

People with SCD should seek immediate medical care if they experience:

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Polycythemia is a condition that causes a person to develop an unusually high number of red blood cells in their body.

According to the United Kingdom’s National Health Service (NHS), this can cause a person’s blood to become thicker, slowing the blood flow.

Some people with polycythemia do not experience symptoms. However, signs of the condition may include:

The NHS recommends people speak with a healthcare professional if these symptoms persist.


Thalassemia is an inherited disorder in which a person’s body does not make enough hemoglobin.

This causes the red blood cells to function unusually and live for a shorter period, leading to fewer healthy red blood cells in the bloodstream.

People with moderate and severe thalassemia often learn they have the condition in childhood. This is generally because they experience symptoms of severe anemia early in life.

A person with a less severe form of thalassemia may only discover they have it if they experience symptoms of anemia or a doctor finds they have anemia during a routine blood test.


Malaria is a potentially life threatening disease that transmits to humans through bites from certain mosquito types.

A parasite causes the infection, and it cannot transmit between people. The parasite multiplies within a person’s red blood cells, destroying the cells.

Symptoms of malaria can be mild or life threatening.

Mild symptoms include:

Severe symptoms of malaria include:

A red blood cell count is a blood test that shows how many red blood cells a person has in their blood.

According to the National Heart, Lung, and Blood Institute, a typical red blood cell count is 5–6 million cells per microliter (cells/mcL) for an adult male and 4–5 million cells/mcL for an adult female.

Several health conditions and other factors can affect a person’s red blood cell count, such as:

Below are some of the most common questions and answers about red blood cells.

What is the main function of red blood cells?

The main function of red blood cells is to transport gases throughout the body.

Red blood cells carry oxygen from the lungs to cells around the body. They also collect carbon dioxide from the body’s cells and transport it back to the lungs. A person then exhales the carbon dioxide.

What raises a person’s red blood cell count?

A person may raise their red blood cell count by eating foods containing iron, such as red meat and green leafy vegetables, or taking iron supplements.

According to the NHS, other factors that may cause a person’s red blood cell count to increase include:

What are the most common blood disorders?

There are several different types of blood disorders. Some common ones include:

Red blood cells carry gases around the body. They collect oxygen from the lungs and transport it to the cells around the body. They then collect carbon dioxide from the cells around the body and transport it back to the lungs.

Several red blood cell disorders can decrease the effectiveness of a person’s red blood cells. These include anemia, polycythemia, sickle cell disease, thalassemia, and malaria.

A person should speak with a healthcare professional if they experience any symptoms that may indicate a red blood cell disorder.