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 and emetophobia. 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. Medications used include antidepressants, benzodiazepines, or beta-blockers.

Specific phobias affect about 6–8% of people in the Western world and 2–4% in Asia, Africa, and Latin America in a given year. Social phobia affects about 7% of people in the United States and 0.5–2.5% of people in the rest of the world. Agoraphobia affects about 1.7% of people. Women are affected by phobias about twice as often as men. The typical onset of a phobia is around 10–17, and rates are lower with increasing age. Those with phobias are more likely to attempt suicide.