system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How are phobias acquired?

What happens on a physiological level that causes such an irrational conditioning to form?
gpt
It's kinda like a psychological allergy. With an allergy, your immune system is overdoing a normal healthy response. A phobia is when generally healthy fears are exaggerated. 

When you have a phobia of something you shouldn't be scared of, there's normally a situational association. Like if you got lost when you were young and when trying to find your mom you got really scared by a cat. Now your scared of cats. These phobias can often be treated with exposure therapy.

Most interesting are non-associative phobias, which are thought to be genetic because they establish themselves the very first time you're exposed to something.