They are usually the result of a frightening or stressful event in early childhood, the teen years or early adulthood. Having a parent who is phobic about something can trigger it in the child. It can be due to genetics, life experiences or brain chemistry. Also evolutionary development may be involved. It's complicated. Do you have a phobia that has actually interfered with your life? Limited you in some way? Fear of heights, open spaces, small spaces, crowds, spiders, water. You name it someone could be phobic about it.