In the twenty-first century, life is different thanks to the four public health innovations of the nineteenth and twentieth centuries, and so disease is different too. But our twenty-first-century illnesses are not simply another layer of ill-health, hidden beneath infectious disease, but an alternative set of conditions, created by the way we live now. We have established four things. First, our twenty-first-century illnesses often arise in the gut, and are associated with the immune system. Second, they strike young, often in children, teenagers and young adults, and many affect more women than men. Third, these illnesses occur in the Western world, but are now on the rise in developing countries as they modernise. Fourth, the rise began in the West in the 1940s, and developing countries followed suit later - Alanna Collen "10% Human: How Your Body's Microbes Hold the Key to Health and Happiness." Harper (May 5, 2015).