Some phobias develop when someone has a scary experience with a particular thing or situation. A tiny brain structure called the amygdala(pronounced: uh-mig-duh-luh) keeps track of experiences that trigger strong emotions. Once a certain thing or situation triggers a strong fear reaction, the amygdala warns the person by triggering a fear reaction every time he or she encounters (or even thinks about) that thing or situation.
For example, someone might develop a bee phobia after being stung during a particularly scary situation. For that person, looking at a photograph of a bee, seeing a bee from a distance, or even walking in a place where there could be a bee can all trigger the phobia.
Sometimes, though, there may be no single event that causes a particular phobia. Some people may be more sensitive to fears because of personality traits they are born with, certain genes they've inherited, or situations they've experienced. People who have had strong childhood fears or anxiety may be more likely to have one or more phobias.