The aim of the paper is to clarify the concept of scientific ignorance: what is it, what are its sources, and when is it epistemically detrimental for science. I present a taxonomy of scientific ignorance, distinguishing between intrinsic and extrinsic sources. I argue that the latter can create a detrimental epistemic gap, which have significant epistemic and social consequences. I provide three examples from medical research to illustrate this point. To conclude, I claim that while some types of scientific ignorance are inevitable and even desirable, other types of scientific ignorance are epistemically and ethically flawed and should be prevented.