How do horror films scare people?

The purpose of a horror film is to scare the audience. The main features in a horror film that scares the audience are being jumpy - making the audience jump, usually accomplished by loud noises following a period of silence, or sudden jump cuts.
Another way of scaring the audience is to use gore; blood, torture and pain usually feature in horror films in order to make the audience feel squeamish.
Linking to jumpy films, suspense is a successful way to scare the audience. A lot of the time horror films trick the audience by building up suspense, suspending to nothing. Although nothing scary happens, the anticipation is enough to scare audiences.
My horror film has used many of these conventions. The use of blood on the mans face is gory, the sudden appearence of the man and the loud music makes the film jumpy, and the build up of suspense through normality with scaty music, and the music getting faster also creates this horror environment.