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It is not well understood what causes specific phobias, although genetics appear to play a role and scientists are working to identify which genes may affect anxiety and fearfulness. In addition, environmental factors may play a role. For instance, children may learn certain phobias from observing the reactions of their parents and others to certain stimuli – seeing a parent recoil from a snake is likely to give the child a fear of snakes.

Researchers also believe that biochemical factors may influence development of phobias. A neurotransmitter called serotonin helps regulate mood and emotions, and it is believed that an imbalance of this biochemical may help cause phobias.

The structure of the brain may also be partly responsible for phobias. The amygdala, which is located deep inside the brain, appears to be responsible for controlling the fear response. People with an overactive amygdala may have heightened anxiety.

Certain phobias tend to occur more in one gender than another, and at different ages. Both social phobia and specific phobias, for instance, tend to begin in childhood or adolescence. Specific phobias are most likely to begin in childhood, around age 7, whereas the incidence of social phobia peaks in the middle teens.