Negative experiences with horses during one's childhood may give rise to this phobia. Equinophobia may also be triggered by a fall from a horse. In many cases, people begin to avoid horses and this gradually develops from fear to a full-blown phobia.

The phobia can also be caused by a simple fear of the animal itself. A horse's imposing size and weight and large teeth may scare some people, especially children.

Negative media portrayals of horses and stallions may add to one's fears.

Equinophobia or hippophobia is a psychological fear of horses. "Equinophobia" is derived from the Greek word φόβος ("phóbos"), meaning "fear" and the Latin word "equus", meaning "horse". The term "hippophobia" is also derived from the Greek word "phóbos" with the prefix derived from the Greek word for horse, ἵππος ("híppos").

An example of the phobia can be found in Freud's psychoanalytic study of Little Hans.