Fear is a number of chain reactions in the brain that occurs when one encounters a potentially harmful stimulus. The amygdala is the part of the brain that receives information from many parts of the brain and interprets this information to generate the emotion of fear. When the amygdala generates a fear emotion, it transmits impulses to the hypothalamus. The hypothalamus then sends impulses to many numbers of different parts of the body to trigger a fight-or-flight response. Fear hormones are secreted by the adrenal gland. The effect of adrenaline (epinephrine) is increasing heart rate, hypocapnia and declines blood flow to the brain. The effect of cortisol is increasing blood glucose levels by converting stored glycogen and fats into blood sugar. It also suppresses the immune system and causes inflammation. The prime cause of cancer is increasing the amounts of ROS in healthy cells. The aim of this review is to show the effect of chronic fear on the cause of cancer in humans by reviewing related clinical studies and biochemistry of fear and cancer. The role of fear, adrenaline and cortisol in causing the hypoxia in tissues is mentioned in this article.