Life in contemporary society is increasingly stressful, and the body is unconsciously exposed to various stressors involving physical, biological, chemical, and social/psychological factors. Exposure to these stressors causes definite biological responses in the body, termed ‘general adaptation syndrome’. Rapid endocrine responses are among the most important reactions following exposure to stressors. These include glucocorticoid and catecholamine secretion into the bloodstream, and are initial biological responses to the stressors. These responses are necessary for the ‘fight-or-flight’ response and must often occur rapidly for the organism to survive. Most biological events, including rapid endocrine responses, also exert effects on circadian rhythms. Indeed, disruption of biological circadian events contributes to numerous diseases, including psychological disorders, immunopathy, serious disorders of the eye, and increases in the incidence of metabolic syndrome components such as obesity, type 2 diabetes, and dyslipidemia. There is increasing evidence that exposure to stressors can affect the amplitude and/or cycle of biological circadian rhythms, and consequently aggravate and/or provoke adverse diseases. In this review, we provide an overview of the relationship between stressors and the stress response, based mainly on results from animal studies. The effects of environmental and social stressors on circadian rhythm are also discussed.