Sci-fi and horror are two genres that often go hand in hand, but it takes skill for authors to perfectly blend these story types in their books. There’s usually a significant overlap between horror and sci-fi fans, as the genres elevate each other and focus on similar themes. Questions of what it means to be human and the horrible actions people take in the face of fear feature prominently in both horror and science fiction. In a novel that successfully mixes both, there must be equal weight given to what makes them different and what brings them together.

https://screenrant.com/books-blend-sci-fi-horror-genres/