Hemophilia is much more common in males than in females. According to the CDC, an estimated 400 male babies are born with hemophilia each year in the United States.

Hemophilia is a rare bleeding disorder that is passed down genetically through families. Having this disorder means you have low levels of certain blood clotting proteins, which impair your blood’s ability to clot properly and stop bleeding.

Blood clotting proteins include:

  • Factor VIII: Low levels of this protein are associated with Hemophilia A
  • Factor IX: Low levels of this protein are associated with Hemophilia B
  • Factor XI: Low levels of this protein are associated with Hemophilia C

The severity of hemophilia is determined by how low the levels of these proteins are in your blood. The lower the level, the more severe the hemophilia, according to the Centers for Disease Control and Prevention (CDC).

People with hemophilia may experience excessive bleeding after an injury, surgery, or for no reason at all, so working with a doctor is important to treat this disorder.

This article explores what we know — and don’t know — about the prevalence of this inherited bleeding disorder.

Language matters

You’ll notice that the language used to share stats and other data points in this article is pretty binary, fluctuating between the use of “male” and “female” or “men” and “women.” Although we typically avoid language like this, specificity is key when reporting on research participants and findings.

Unfortunately, the studies and surveys referenced in this article didn’t report data on, or include, participants who were transgender, nonbinary, gender nonconforming, genderqueer, agender, or genderless.

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Hemophilia is much more common in people assigned male at birth because of how genes are passed to males vs. females. In fact, according to the CDC, about 400 male babies are born with hemophilia A each year in the United States. Haemophilia A is the most common type of hemophilia.

It’s not known exactly how many people in the United States have hemophilia. However, according to data collected between 2012 and 2018, it’s estimated that about 33,000 males in the United States are living with the disorder.

Unfortunately, it’s not known how many people assigned female at birth are living with hemophilia in the United States. Hemophilia can have unique complications for women, as it can affect reproductive health, so this is an important area of research.

That said, a 2021 study did look at data that shows the number of women who sought treatment at a hemophilia medical center in the United States between 2012 and 2020, and found that about 1,700 women and girls met the criteria for the disorder.

For comparison, about 23,000 men and boys received treatment for hemophilia at one of those centers during that same time period.

According to a 2019 meta-analysis, about 1,125,000 men around the world are living with hemophilia. Prior to that study, it was thought that only about 400,000 people worldwide had the disorder.

Again, there are no figures for how many women are living with hemophilia across the world, and more research is necessary.

The cause of hemophilia is a genetic mutation on the X chromosome, which is responsible for making the proteins that are necessary for blood clotting. Since these genetic mutations occur on the X chromosome passed down from parents, it puts men at greater risk for inheriting this disorder.

Why are men at more risk?

Men receive an X chromosome from their mother and a Y chromosome from their father. If the X chromosome they receive from their mother has a genetic mutation associated with hemophilia, they will inherit the disorder.

Women, on the other hand, receive two X chromosomes, one from their mother and one from their father.

Both X chromosomes would need to have genetic mutations associated with hemophilia for the disorder to show up in that person. Or one X chromosome would need to be affected while the other is missing or non-functioning, according to the CDC.

However, having just one affected X chromosome makes that person a carrier and able to pass the disorder to their children.

It’s also important to note that hemophilia affects people of all racial and ethnic backgrounds. In some rare instances, people develop the disorder later in life or are young women who have recently given birth. In these cases, treatment usually resolves the condition, according to the CDC.

Hemophilia is a rare, inherited bleeding disorder that affects blood clotting. People with the condition are at higher risk of excessive bleeding.

Men are more likely to inherit this disorder than women because the genetic mutations that cause hemophilia are located on the X chromosome that’s passed from parent to child.

It’s not known exactly how many women are living with hemophilia, but more research is necessary to help identify and treat women with this condition, as it can affect reproductive health.

With proper treatment, people with hemophilia can live long, healthy lives.