There are many websites that provide lists of the most common fears among adults, such as Psychology.About.com, WebMD.com, Forbes.com and ABC.net.au. Each one varies slightly as to the exact rankings of different phobias, but agoraphobia, social phobias, arachnophobia and acrophobia are in all the lists.
On About.com, some of the most common objects of phobias listed are spiders, snakes, heights, crowded spaces and dogs. More common objects causing phobias are thunder and lightning, injections, social situations, flying and germs. Forbes notes that most fears have basis in evolution. Fears such as those of enclosed spaces or of spiders and snakes make sense because these are things that put humans in danger or expose them to predators. This explains why fears of dangerous creatures or situations top the lists.
However, there are also a lot of common fears that are irrational or excessive in nature. Robert Leahy, according to Forbes, says that we live in the "age of anxiety," in which anxiety disorders have risen dramatically compared to previous years. It is possible that this is due to the breakdown of communities and relationships in today's society, as evidenced by the growing divorce rate. Some of these irrational phobias may also be caused by unpleasant experiences with the stimulus in the past, especially during childhood, notes About.com.