Phobias are persistent, irrational fears of objects or situations that persist even though the fear has no base in current reality. 

People with phobias may experience intense mental and physical symptoms when exposed to something that triggers their phobia. In addition to feeling intense anxiety and fear, they may sweat, develop rapid heartbeat, have breathing difficulties and experience other symptoms that may escalate to a full-blown panic attack (a sudden, brief episode of fear and anxiety).

There are three major types of phobias:

• Specific phobia. Also known as simple phobia, it is diagnosed in people who have phobias associated with specific objects or situations (e.g., animals, elevators) that do not have intrinsic danger.
  
  
• Social phobia. Diagnosed in people who have extreme anxiety in certain social and public situations.
  
  
• Agoraphobia. Diagnosed in people whose fears cause them to avoid most or all situations which involve leaving their home.

It is not well understood what causes phobias, although genetics, biology and biochemical factors all appear to play a role. In many cases, phobias are a symptom of anxiety disorders or other mental illnesses such as depression, substance abuse or eating disorders. Some phobias (e.g., simple phobia) begin in childhood whereas others (e.g., social phobia) often begin during the teen years. Phobias often peak during the 20s.