phobia phobia 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. phobiathe fear of spiders is one of the most common phobias.specialtypsychiatry, clinical psychologysymptomsfear of an object or situationcomplicationssuicide, high risk of comorbiditiesusual onsetrapiddurationmore than six monthstypesspecific phobias, social anxiety disorder, agoraphobiacausesgenetic and environmental factorstreatmentexposure therapy, counselling, medicationmedicationantidepressants, benzodiazepines, beta-blockersfrequencyspecific phobias: ~5%social phobia: ~5%agoraphobia: ~2% 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. classification fear is an emotional response to a current perceived danger. this differs from anxiety which is a response in preparation of a future threat. fear and anxiety often can overlap but this distinction can help identify subtle differences between disorders, as well as differentiate between a response that would be expected given a person's developmental stage and culture. icd-11 the international classification of diseases (11th version: icd-11) is a globally used diagnostic tool for epidemiology, health management and clinical purposes maintained by the world health organization (who). the icd classifies phobic disorders under the category of mental, behavioural or neurodevelopmental disorders. the icd-10 differentiates between phobic anxiety disorders, such as agoraphobia, and other anxiety disorders, such as generalized anxiety disorder. the icd-11 merges both groups together as anxiety or fear-related disorders. dsm-5 most phobias are classified into 3 categories. according to the diagnostic and statistical manual of mental disorders, fifth edition (dsm-5), such phobias are considered subtypes of anxiety disorder. 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. environmental rachman proposed three pathways for the development of phobias: direct or classical conditioning (exposure to phobic stimulus), vicarious acquisition (seeing others experience phobic stimulus), and informational/instructional acquisition (learning about phobic stimulus from others). classical conditioning much of the progress in understanding the acquisition of fear responses in phobias can be attributed to classical conditioning (pavlovian model). when an aversive stimulus and a neutral one are paired together, for instance, when an electric shock is given in a specific room, the subject can start to fear not only the shock but the room as well. in behavioral terms, the room is a conditioned stimulus (cs). when paired with an aversive unconditioned stimulus (ucs) (the shock), it creates a conditioned response (cr) (fear for the room) (cs+ucs=cr). for example, in case of the fear of heights (acrophobia), the cs is heights. such as a balcony on the top floors of a high rise building. the ucs can originate from an aversive or traumatizing event in the person's life, such as almost falling from a great height. the original fear of nearly falling is associated with being high, leading to a fear of heights. in other words, the cs (heights) associated with the aversive ucs (almost falling) leads to the cr (fear). though historically influential in the theory of fear acquisition, this direct conditioning model is not the only proposed way to acquire a phobia. this theory in fact has limitations as not everyone that has experienced a traumatic event develops a phobia and vice versa. vicarious conditioning vicarious fear acquisition is learning to fear something, not by a subject's own experience of fear, but by watching others, oftentimes a parent (observational learning). for instance, when a child sees a parent reacting fearfully to an animal, the child can also become afraid of the animal. through observational learning, humans can learn to fear potentially dangerous objects—a reaction observed in other primates. a study on non-human primates, showed that the primates learned to fear snakes at a fast rate after watching parents' fearful reactions. an increase in fearful behaviours was observed as the non-human primates observed their parents' fearful reactions. although observational learning has proven effective in creating reactions of fear and phobias, it has also been shown that by physically experiencing an event, increases the chance of fearful and phobic behaviours. in some cases, physically experiencing an event may increase the fear and phobia more than observing a fearful reaction of another human or non-human primate. informational/instructional acquisition informational/instructional fear acquisition is learning to fear something by getting information. for instance, fearing electrical wire after hearing that touching it causes an electric shock. a conditioned fear response to an object or situation is not always a phobia. there must also be symptoms of impairment and avoidance. impairment is defined as an inability to complete routine tasks, whether occupational, academic, or social. for example, an occupational impairment can result from acrophobia, from not taking a job solely because of its location on the top floor of a building, or socially not participating in an event at a theme park. the avoidance aspect is defined as behaviour that results in the omission of an aversive event that would otherwise occur, intending to prevent anxiety. genetic main article: epigenetics of anxiety and stress–related disorders with the completion of the human genome project in 2003, much research has been completed looking at specific genes that may cause or contribute to medical conditions. candidate genes were the focus of most of these studies until the past decade, when the cost and ability to perform genome-wide analyses became more available. the glrb gene was identified as a possible target for agoraphobia. an area still in development is reviewing epigenetic components or the interaction of the environment on genes through methylation. a number of genes are being examined through this epigenetic lens which may be linked with social anxiety disorder, including maoa, crhr1, and oxtr. each phobia related disorder has some degree of genetic susceptibility. those with specific phobias are more likely to have first degree relatives with the same specific phobia. similarly, social anxiety disorder is found two to six times more frequently in those with first degree relatives that have it versus those that do not. agoraphobia is believed to have the strongest genetic association. mechanism regions of the brain associated with phobias anatomical components of the limbic system limbic system beneath the lateral fissure in the cerebral cortex, the insula, or insular cortex, of the brain has been identified as part of the limbic system, along with the cingulated gyrus, hippocampus, corpus callosum, and other nearby cortices. this system has been found to play a role in emotion processing, and the insula, in particular, may contribute to maintaining autonomic functions. studies by critchley et al. indicate the insula as being involved in the experience of emotion by detecting and interpreting threatening stimuli. similar studies monitoring insula activity have shown a correlation between increased insular activation and anxiety. in the frontal lobes, other cortices involved with phobia and fear are the anterior cingulate cortex and the medial prefrontal cortex. in the processing of emotional stimuli, studies on phobic reactions to facial expressions have indicated that these areas are involved in the processing and responding to negative stimuli. the ventromedial prefrontal cortex has been said to influence the amygdala by monitoring its reaction to emotional stimuli or even fearful memories. most specifically, the medial prefrontal cortex is active during the extinction of fear and is responsible for long-term extinction. stimulation of this area decreases conditioned fear responses, so its role may be in inhibiting the amygdala and its reaction to fearful stimuli. the hippocampus is a horseshoe-shaped structure that plays an essential part in the brain's limbic system. this is because it forms memories and connects them with emotions and the senses. when dealing with fear, the hippocampus receives impulses from the amygdala that allow it to connect the fear with a certain sense, such as a smell or sound. amygdala the amygdala is an almond-shaped mass of nuclei located deep in the brain's medial temporal lobe. it processes the events associated with fear and is linked to social phobia and other anxiety disorders. the amygdala's ability to respond to fearful stimuli occurs through fear conditioning. like classical conditioning, the amygdala learns to associate a conditioned stimulus with a negative or avoidant stimulus, creating a conditioned fear response often seen in phobic individuals. the amygdala is responsible for recognizing certain stimuli or cues as dangerous and plays a role in the storage of threatening stimuli to memory. the basolateral nuclei (or basolateral amygdala) and the hippocampus interact with the amygdala in-memory storage. this connection suggests why memories are often remembered more vividly if they have emotional significance. in addition to memory, the amygdala also triggers the secretion of hormones that affect fear and aggression. when the fear or aggression response is initiated, the amygdala releases hormones into the body to put the human body into an "alert" state, which prepares the individual to move, run, fight, etc. this defensive "alert" state and response are known as the fight-or-flight response. however, inside the brain, this stress response can be observed in the hypothalamic-pituitary-adrenal axis (hpa). this circuit incorporates the process of receiving stimuli, interpreting them, and releasing certain hormones into the bloodstream. the parvocellular neurosecretory neurons of the hypothalamus release corticotropin-releasing hormone (crh), which is sent to the anterior pituitary. here the pituitary releases adrenocorticotropic hormone (acth), which ultimately stimulates the