Could the food we eat and the air we breath be damaging our immune systems? The number of people with autoimmune diseases, from rheumatoid arthritis to type 1 diabetes, began to increase around 40 years ago in the west. Now, some are also emerging in countries that had never seen the diseases before. Ian Sample speaks to genetic scientist and consultant gastroenterologist James Lee about how this points to what western lifestyles might be doing to our health, and how genetics could reveal exactly how our immune systems are malfunctioning. Help support our independent journalism at theguardian.com/sciencepod