Women are more than two times as likely as men to be diagnosed with an anxiety disorder. (6) It’s not clear why this is the case, but researchers have theorized that it may be due to a combination of social and biological factors. Scientists are still investigating the complex role that sex plays in brain chemistry, but some research suggests that in women, the amygdala, which is the part of the brain responsible for processing potential threats, may be more sensitive to negative stimuli and may hold on to the memory of it longer. (7) 
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Genetics and family history (e.g. parental anxiety) may put an individual at increased risk of an anxiety disorder, but generally external stimuli will trigger its onset or exacerbation.[57] Estimates of genetic influence on anxiety, based on studies of twins, range from 25-40% depending on the specific type and age-group under study. For example, genetic differences account for about 43% of variance in panic disorder and 28% in generalized anxiety disorder.[58] Longitudinal twin studies have shown the moderate stability of anxiety from childhood through to adulthood is mainly influenced by stability in genetic influence.[60][61] When investigating how anxiety is passed on from parents to children, it is important to account for sharing of genes as well as environments, for example using the intergenerational children-of-twins design.[62]
The degree of accompanying stress response and its physiological, psychological, and emotional changes are directly proportional to the degree of anxiety. For example, if you are only slightly concerned, such as being slightly nervous about meeting someone new, the body produces a small degree stress response. The small degree stress response can be so slight that you don’t even notice it.