A phobia can develop at any age from childhood to early adulthood. Often, they are related to a frightening or stressful event, however there is not always a clear reason they occur.
Complex phobias generally develop during adulthood and are usually linked to an extended fear about a particular situation or circumstance.
There is not one set cause for phobias, but there are several factors that are associated with the increased likelihood of the development of phobias:
Experience of an early negative experience, incident or trauma related to the phobic stimuli
Learning from a family member
Genetic predisposition, shown in family history of anxiety
Evolutionary reason for fear may increase likelihood