Best answer is the what is the relationship between stress and illness? a. the only relationship between stress and illness has to do with the effects of tension on blood pressure. b. stress can trigger certain illnesses, reduce the body’s ability to fight an illness, and make some diseases harder to control. c. prolonged stress can make a person tired, but it has no harmful effects on the immune system. d. when stress causes the fight-or-flight response, it increases the body’s ability to fight an illness.