Billions of people worldwide suffer from some kind of allergy and this is the focus of Theresa MacPhail’s book, Allergic. As a medical anthropologist and allergy sufferer herself she looks back at the history of diagnosis and treatment and investigates the worrying increase in numbers. It's thought by 2030 half the population will be sufferers. James Kinross is a colorectal surgeon and suggests that some of the answer as to why there’s been a rise in allergies lies in the imbalance of our microbiome - our inner ecosystem of viruses, bacteria and other microbes. In his book, Dark Matter, he argues that the microbiome is under threat from our modern lifestyles, the food we consume, and the air we breathe. Fermented foods are now thought to be integral to a healthy gut because they provide a vast amount of natural probiotics which can boost immunity and soothe the digestive tract. Johnny Drain is a materials scientist and a chef who believes in the benefits of fermentation, and has looked worldwide for innovations in techniques and flavours. Producer: Natalia Fernandez