Sickle cell disease and sickle cell trait: What to know and why it matters

Published May 7, 2026

Sickle cell disease is a lifelong condition that affects the blood, the body, and overall health. For every person living with sickle cell disease in the US, about 30 people carry the trait, and most don’t know they do. This article explores what both mean, how they’re different, and why it matters.¹⁻³

What is sickle cell disease?

Sickle cell disease is a group of inherited blood disorders that affect hemoglobin, the oxygen-carrying protein inside red blood cells. Typically, red blood cells are round, soft, and flexible. They bend and move easily through even the smallest blood vessels to deliver oxygen throughout the body. In sickle cell disease, hemoglobin can cause red blood cells to become stiff, sticky, and sickle-shaped, which can lead to serious complications.¹

About 100,000 people in the US and 8 million people worldwide live with sickle cell disease. While it can affect anyone, it’s most common in people with ancestry from sub-Saharan Africa, India, the Middle East, South America, Central America, the Caribbean, and the Mediterranean.¹

Is sickle cell disease the same as sickle cell anemia?

Sickle cell disease is the broader term for a group of inherited blood disorders that cause red blood cells to become sickled. Sickle cell anemia is one type within that group, and it’s the most common and often most severe form.¹

What causes sickle cell disease?

Sickle cell disease is a lifelong condition a person is born with. It’s caused by inherited gene changes that affect how hemoglobin is made. In the US, it’s most often found during newborn screening, and about 2,000 babies are born with it each year.⁴

Everyone inherits 2 copies of a gene called HBB, 1 from each parent. These genes tell the body how to make hemoglobin. People with sickle cell disease inherit gene changes from both parents that tell the body to make sickle hemoglobin (hemoglobin S) instead of the typical form, hemoglobin A.

In every type of sickle cell disease, there’s at least 1 gene for hemoglobin S. In some cases, a person inherits 2 genes for hemoglobin S (sickle cell anemia). In others, they inherit 1 gene for hemoglobin S and 1 gene for another type of hemoglobin, such as hemoglobin C.¹,²

What’s the difference between sickle cell trait and sickle cell disease?

The difference comes down to what a person inherits from their parents and how that affects the type of hemoglobin their body makes.

Sickle cell trait occurs when a person inherits 1 gene for hemoglobin A and 1 gene for hemoglobin S. It’s not the same as sickle cell disease, where a person inherits gene changes from both parents that affect how hemoglobin is made.

It’s estimated that up to 3 million people in the US and more than 100 million people worldwide have sickle cell trait. Most people with the trait don’t have symptoms and live healthy, active lives. Having sickle cell trait doesn’t mean a person has sickle cell disease. It means they carry the hemoglobin S gene and can pass it on to their children.³,⁵

When might sickle cell trait testing be relevant for adults?

Many adults don’t know their sickle cell trait status because it often doesn’t cause symptoms. Testing matters when planning for a family, since it helps clarify the chance of passing sickle cell disease to a child. It’s also important if you were never tested at birth or don’t know your status.⁶

How does sickle cell disease affect the body?

Red blood cells are packed with hemoglobin, a protein that influences how those cells behave.

Typically, hemoglobin helps red blood cells stay soft, round, and flexible. But with hemoglobin S, things can change. Under certain conditions, such as stress, low oxygen, dehydration, or extreme cold, it behaves differently. Hemoglobin S can form rigid structures inside red blood cells, causing them to lose their round shape and become stiff, sticky, and sickle-shaped.

Because sickled red blood cells are sticky and don’t bend or move easily, they can clump together and get stuck in small blood vessels. Blood flow can slow or become blocked, preventing oxygen from reaching tissues and organs the way it should. This can lead to severe pain (known as a pain crisis), organ damage, and other serious, potentially life-threatening complications.

These cells are also more fragile and have a much shorter lifespan. While typical red blood cells live for about 120 days, sickled red blood cells live for only about 16 days. This creates a constant shortage of red blood cells (anemia) because the body cannot replace them at the speed they’re being destroyed.

Over time, repeated changes in blood flow and ongoing anemia can place stress on multiple organs, including the lungs, brain, kidneys, eyes, and spleen.

In those with sickle cell disease, daily life may be associated with fatigue, disruptions to work or school, frequent medical visits, ongoing pain, anxiety about complications, and the emotional strain of living with a condition that can become urgent quickly.¹,⁴,⁵