A phobia is an anxiety disorder defined by a persistent and excessive fear of an object or situation. Phobias typically result in a rapid onset of fear and are usually present for more than six months. Those affected go to great lengths to avoid the situation or object, to a degree greater than the actual danger posed. If the object or situation cannot be avoided, they experience significant distress. Other symptoms can include fainting, which may occur in blood or injury phobia, and panic attacks, often found in agoraphobia. Around 75% of those with phobias have multiple phobias.Phobias can be divided into specific phobias, social anxiety disorder, and agoraphobia. Specific phobias are further divided to include certain animals, natural environment, blood or injury, and particular situations. The most common are fear of spiders, fear of snakes, and fear of heights. Specific phobias may be caused by a negative experience with the object or situation in early childhood. Social phobia is when a person fears a situation due to worries about others judging them. Agoraphobia is a fear of a situation due to perceived difficulty or inability to escape.It is recommended that specific phobias be treated with exposure therapy, in which the person is introduced to the situation or object in question until the fear resolves. Medications are not helpful for specific phobias. Social phobia and agoraphobia may be treated with counseling, medications, or a combination of both.
The categories are:

Specific phobias: Fear of particular objects or situations that results in anxiety and avoidance. May lead to panic attacks if exposed to feared stimulus or in anticipation of encounter. A specific phobia may be further subdivided into five categories: animal, natural environment, situational, blood-injection-injury, and other. Agoraphobia: a generalized fear of leaving home or a small familiar safe area and of possible panic attacks that might follow. Various specific phobias may also cause it, such as fear of open spaces, social embarrassment (social agoraphobia), fear of contamination (fear of germs, possibly complicated by obsessive–compulsive disorder) or PTSD (post-traumatic stress disorder) related to a trauma that occurred outdoors. Social anxiety disorder (SAD), also known as social phobia, is when the situation is feared out of a worrying about others judging them. Performance only is a subtype of social anxiety disorder Phobias vary in severity among individuals. Some individuals can avoid the subject and experience relatively mild anxiety over that fear. Others experience full-fledged panic attacks with all the associated impairing symptoms. Most individuals understand that their fear is irrational but cannot override their panic response. These individuals often report dizziness, loss of bladder or bowel control, tachypnea, feelings of pain, and shortness of breath. Causes
There are multiple theories about how phobias develop and likely occur due to a combination of environmental and genetic factors. The degree to whether environment or genetic influences have a more significant role varies by condition, with social anxiety disorder and agoraphobia having around a 50% heritability rate.