Who Gets Inhibitors?

No one knows why some people with hemophilia get inhibitors and others do not.1,3

We do know that between 20% and 30% of patients with hemophilia A develop inhibitors.4

Fewer than 5% of people with hemophilia B develop inhibitors.4

Chances of Inhibitors

There are some things that may increase the chances that an inhibitor will develop.1,5


  • A family history of inhibitors1,5
  • African or Latino heritage1,5
  • Severe hemophilia (as opposed to mild or moderate hemophilia)4
  • People with hemophilia with large genetic mutations1,8


  • Inhibitors tend to happen early in treatment, usually within the first 10-20 days after starting factor replacement treatment.5
  • Inhibitors tend to appear after surgery and intensive factor replacement treatments with high doses.17


  • Inhibitors usually develop before the age of 5 years, after having received a few factor replacement treatments.1,17

The general risk guidelines show a higher chance of children with severe hemophilia developing inhibitors. Yet, the truth is, inhibitors cannot be prevented and they can happen at any time.1,17