Billions of people worldwide have some form of allergy. And over the past decade, the number of people diagnosed with allergy has been steadily increasing. Medical anthropologist Theresa MacPhail, herself an allergy sufferer, sets out to understand why. The result is a holistic and deeply researched examination of allergies, from their first medical description in 1819 to the mind-bending new treatments that are giving patients hope. MacPhail spent years interviewing hundreds of experts, patients and activists. Pollution, chemicals, antibiotics and, increasingly, climate change are all making our immune systems become more and more irritated. But, as she shows us, understanding what is irritating us and why will help us to craft better environments in the future-so we can all breathe easier.