A phobia is an intense fear reaction to a particular thing or a situation. With a phobia, the fear is out of proportion to the potential danger. But to the person with the phobia, the danger feels real because the fear is so very strong. Phobias cause people to worry about, dread, feel upset by, and avoid the things or situations they fear because the physical sensations of fear can be so intense. So having a phobia can interfere with normal activities.