The immune system is also affected by stress. Dr. Esther M. Sternberg at NIH’s National Institute of Mental Health says it makes sense for the immune system to gear up and get ready to heal potential wounds. But chronic stress can cause the system to backfire. Research has shown that wounds in people under chronic stress heal more slowly. Caregivers of people with Alzheimer’s disease, who are often under great stress, are more likely to get the flu or a cold—and when they take vaccines to protect their loved ones from getting flu, their bodies don’t respond as well.