This (4:15 mins) video by Madhumita Murga explains how a lack of nurturing when we are young can limit our ability to cope with stress and creates changes to the way our DNA is expressed. These changes are passed on to future generations resulting in them having a sensitivity to stress.
Chronic stress damages the brain in several ways, which are explained in the video. The good news is that the damage can be reversed by releasing the stress and healing the trauma that caused it. Many stress reduction techniques can help including exercise and meditation, while therapies like Psych-K and Family Constellations can assist in healing any trauma and emotional pain underneath it.