Final answer:
Stressful situations lead to the release of stress hormone cortisol, which can weaken the immune system and lead to illness.
Step-by-step explanation:
Stressful situations can lead to disease because they cause the release of stress hormones. One of the main stress hormones released is cortisol. When a person experiences stress, the hypothalamus in the brain releases corticotropin-releasing factor, which triggers the release of adrenocorticotropic hormone (ACTH) from the pituitary gland. ACTH then activates the adrenal glands to secrete cortisol, which affects various bodily processes and prepares the person for fight-or-flight response. However, sustained elevated levels of cortisol weaken the immune system and can lead to illness.