A phobia is an irrational, persistent fear of certain situations, objects, activities, or persons. The main symptom of this disorder is the excessive, unreasonable desire to avoid the feared subject. When the fear is beyond one's control, or if the fear is interfering with daily life, then a diagnosis under one of the anxiety disorders can be made.

Phobias (in the clinical meaning of the term) are the most common form of anxiety disorders. An American study by the National Institute of Mental Health (NIMH) found that between 8.7% and 18.1% of Americans suffer from phobias. Broken down by age and gender, the study found that phobias were the most common mental illness among women in all age groups and the second most common illness among men older than 25.

It is generally accepted that phobias arise from a combination of external events and internal predispositions. Some phobias such as arachnophobia (fear of spiders) and ophidiophobia (fear of snakes) however, may arise more easily due to an evolutionary trait that conditioned humans to fear certain creatures that could cause them harm. In a famous experiment, Martin Seligman used classical conditioning to establish phobias of snakes and flowers. The results of the experiment showed that it took far fewer shocks to create an adverse response to a picture of a snake than to a picture of a flower, leading to the conclusion that certain objects may have a genetic predisposition to being associated with fear. Many specific phobias can be traced back to a specific triggering event, usually a traumatic experience at an early age. Social phobias and agoraphobia have more complex causes that are not entirely known at this time. It is believed that heredity, genetics, and brain chemistry combine with life-experiences to play a major role in the development of anxiety disorders and phobias.

Clinical phobias

Most psychologists and psychiatrists classify most phobias into three categories:

1) Social phobias - fears involving other people or social situations such as performance anxiety or fears of embarrassment by scrutiny of others, such as eating in public. Social phobias may be further subdivided into:
* the general social phobia, also known as social anxiety disorder, and
* specific social phobias, which are cases of anxiety triggered only in specific situations. The symptoms may extend to psychosomatic manifestation of physical problems. For example, sufferers of paruresis find it difficult or impossible to urinate in reduced levels of privacy. That goes beyond mere preference. If the condition triggers, the person physically cannot empty their bladder.

2)Specific phobias - fear of a single specific panic trigger such as spiders, dogs, elevators, water, flying, catching a specific illness, etc.

3) Agoraphobia - a generalized fear of leaving home or a small familiar 'safe' area, and of possible panic attacks that might follow. Agoraphobia is the only phobia regularly treated as a medical condition.

According to the Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition (DSM-IV), social phobia, specific phobia, and agoraphobia are sub-groups of anxiety disorder.

Many of the specific phobias, such as fear of dogs, heights, spiders and so forth, are extensions of fears that a lot of people have. People with these phobias specifically avoid the entity they fear.

Phobias vary in severity among individuals. Some individuals can simply avoid the subject of their fear and suffer only relatively mild anxiety over that fear. Others suffer fully-fledged panic attacks with all the associated disabling symptoms. Most individuals understand that they are suffering from an irrational fear, but are powerless to override their initial panic reaction.

Source : www.wikipedia.org