Signs and symptoms
Fear, discomfort or anxiety may be triggered both by the presence and the anticipation of the specific object or situation. The main behavioral sign of a specific phobia is avoidance. The fear or anxiety associated with specific phobia can also manifest in physical symptoms such as an increased heart rate, shortness of breath, muscle tension, sweating, or a desire to escape the situation. Causes
The exact cause of specific phobias is not known. The mechanisms for development of specific phobias can be distinguished between innate (genetic and neurobiological) factors, and learned factors. In neurobiology, one explanation proposed for specific phobia is that the typical activation of the amygdala in response to stimuli may be exaggerated due to pathological changes. According to this theory, a deficiency in amygdala habituation may also contribute to the persistence of non-experiential phobia. Certain phobias that are less lethal (e.g. dogs) seem to be more frequently observed and easily acquired in comparison to potentially lethal fears which are more relevant to developed human society (e.g. cars and guns). This was theorised to be due to biological adaptation being passed through evolution which makes recent threats less prone to easy acquisition. However, a 2014 study found evidence against this evolutionary theory, which stated: "Our findings are inconsistent with the hypothesis that fears/phobias of individual stimuli result from genetic and environmental factors unique to that stimulus. Instead, we observed substantial sharing of risk factors across individual fears."
There is an additional peak in incidence, reaching nearly 1% per year, during old age in both men and women, possibly reflective of newly occurring physical conditions or adverse life events. The development of phobias varies with subtypes, with animal and blood injection phobias typically beginning in childhood (ages 5–12), whereas development of situational specific phobias (i.e., fear of flying) usually occurs in late adolescence and early adulthood.In the US, the lifetime prevalence rate is 12.5% and a one-year prevalence rate of 9.1%. An estimated 12.5% of U.S. adults experience specific phobia at some time in their lives and the prevalence is approximately double in females compared to males. An estimated 19.3% of adolescents experience specific phobia, but the difference between males and females is not as pronounced. See also
List of phobias
Phobia

References
External links
Encyclopedia of Mental Disorders – Specific phobias