Social isolation and loneliness can even change your genes. Social isolation, loneliness, and depression affect gene expression, causing increased inflammation in the brain and decreased production of antiviral interferon. Lonely people have increased activation of the HPA axis, causing them to be hypervigilant about social threats. They might believe that most people in the world are out to harm them, humiliate them, or behave derisively or dismissively toward them. In this respect chronically lonely people resemble people with PTSD.
