Sickle cell disease is not exclusive to Black people, but it disproportionately affects them. In the United States, more than 90% of people with sickle cell disease are non-Hispanic Black or African American. The disease also occurs in Hispanic, Mediterranean, Middle Eastern, and Indian populations. The reason it clusters in these groups has nothing to do with race itself and everything to do with geography: sickle cell trait evolved as a defense against malaria in regions where the parasite was historically deadly.
Why Sickle Cell Is Linked to Certain Populations
Sickle cell disease traces back to a single genetic mutation that changes the shape of hemoglobin, the protein in red blood cells that carries oxygen. This mutation arose independently in several parts of the world where malaria was a major killer: sub-Saharan Africa, the Arabian Peninsula, India, and Mediterranean countries like Greece, Turkey, and Italy.
Carrying one copy of the mutated gene (sickle cell trait) provides a real survival advantage against malaria. When the malaria parasite invades a red blood cell that contains the altered hemoglobin, the hemoglobin stiffens and polymerizes in the low-oxygen environments found in organs like the bone marrow, brain, and liver. This stalls the parasite’s growth before it can replicate, effectively protecting the carrier. Over thousands of years, natural selection favored people who carried one copy of the gene in malaria-endemic regions, making the trait more common in those populations.
The key point: sickle cell follows the historical map of malaria, not the boundaries of any race. It became concentrated in populations from malaria-prone areas, and because sub-Saharan Africa carried the heaviest malaria burden, people of African descent carry the trait at the highest rates.
Who Gets Sickle Cell Disease Today
In the U.S., sickle cell disease occurs in about 1 out of every 365 Black or African American births. It also occurs in about 1 out of every 16,300 Hispanic American births. An estimated 3% to 9% of Americans with sickle cell disease are Hispanic or Latino. Globally, the disease affects millions and is common among people whose ancestors came from Spanish-speaking regions in the Western Hemisphere (South America, the Caribbean, Central America), Saudi Arabia, India, and Mediterranean countries.
Two parents who each carry one copy of the mutated gene have a 25% chance with each pregnancy of having a child with sickle cell disease. The condition is autosomal recessive, meaning it sits on a non-sex chromosome and requires two copies of the altered gene to cause disease. A person with just one copy (sickle cell trait) typically has no symptoms but can pass the gene to their children.
How Sickle Cell Became a “Black Disease”
The association between sickle cell and Black people was forged in the earliest days of medical research on the condition. The first documented case, published in 1910 by James B. Herrick, described a patient named Walter Clement Noel, whom Herrick identified as “an intelligent negro.” The second case in 1911 described a woman with “facies characteristic of her race.” By the third published case in 1915, researchers were confidently listing the patients’ Black racial identity as one of the defining similarities between cases.
Over the next two decades, this connection hardened into medical dogma. When cases appeared in people who did not appear Black, researchers assumed the patient must have had mixed-race ancestry. In some instances, clinicians actively denied the diagnosis because they believed sickle cell only occurred in Black people. During the mid-1900s, white supremacists even pointed to the disease as biological evidence supporting segregation and anti-miscegenation laws, framing it as proof that Black people were “tainted right down to their genes.”
This racial framing stuck. It shaped public perception, medical education, and even clinical practice in ways that persist today. The consequence is a disease understood primarily through the lens of race rather than evolutionary biology and geography.
The Genetics Behind the Mutation
Sickle cell disease results from variants in the HBB gene, which provides instructions for making beta-globin, one of the building blocks of hemoglobin. The most common variant produces an abnormal version called hemoglobin S (HbS). Other variants in the same gene produce hemoglobin C and hemoglobin E, which can also combine with HbS to cause different forms of sickle cell disease.
When both copies of the HBB gene carry a variant, all of a person’s hemoglobin is abnormal. Under low-oxygen conditions, the altered hemoglobin molecules clump together and distort red blood cells into a rigid, crescent shape. These misshapen cells clog small blood vessels, causing the pain crises, organ damage, and other complications that define the disease. When only one copy is altered, the person produces a mix of normal and abnormal hemoglobin, which is enough to resist malaria but not enough to cause sickle cell disease.
Why the Distinction Matters
Calling sickle cell a “Black disease” creates real problems. It can lead to missed or delayed diagnoses in Hispanic, Arab, Indian, and Mediterranean patients who carry the same genetic mutations. It also reinforces a false idea that race is a reliable biological category, when in reality, the sickle cell gene tracks with ancestral geography, not skin color. A person of Greek or Saudi Arabian descent whose ancestors lived in a malaria zone can carry and pass on the gene just as readily as someone of West African descent.
Sickle cell disease is most common in Black populations, and that fact matters for public health screening and resource allocation. But “most common in” is different from “exclusive to.” Understanding the difference helps ensure that everyone at risk gets appropriate screening, and that the disease is understood for what it actually is: an evolutionary response to one of humanity’s oldest and deadliest infections.