Pollen counts are rising and more of us are experiencing hay fever symptoms than ever before. From airborne allergens to the food on our plates or the chemicals and plants that touch our skin, around 40% of the global population has some form of allergic disease. By 2030, today’s guest reveals, 50% of us will be affected.

Professor Theresa MacPhail is a medical anthropologist and writer, who made it her life’s work to understand more about allergy after her father died following a bee sting. Her book Allergic: How Our Immune System Reacts To A Changing World, is a detailed, enlightening look at the history of allergies and their growth in line with the industrial revolution.

Why are allergies on the rise? Why is it that 200 years ago allergies barely existed, yet today they are in our pets and farm animals? We talk about what actually happens to cause the release of histamine - which is responsible for many of our allergic symptoms. Theresa also covers the main historical theories as to the cause of allergies from the ‘hygiene hypothesis’ to the ‘farmhouse effect’ and the ‘old friends theory’.

What we do know is that allergies occur in the interaction between humans and our environment. Our environment has changed so much over the past 200 years and our immune systems simply cannot keep up. Theresa explains the body’s three main barriers to infection and allergy – our skin, respiratory system and gut. When these barriers are damaged, they become more porous and can let unwanted molecules into our bodies – causing infection, inflammation, or allergy. And what’s damaging them is things like air pollution, diesel fumes, chemicals, antibiotics, to name just a few.

We cover the practical steps we can take to mitigate allergies but there are much wider societal issues that need addressing as well. Theresa explains that we are part of a bigger ecosystem - our bodies are continually making decisions on what they can tolerate and what they can’t. We can try our best to build up our own barriers to tolerate more of the modern environment but the uncomfortable truth is that we collectively have a lot more to do to protect each other and the natural world.

This is a deep dive into a very important topic. My hope is that anyone suffering from allergies will feel seen, and anyone lucky enough not to, will gain more empathy and understanding. I hope you enjoy listening.

*Please note that this conversation refers to studies on mice.

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JAMA: 2010-08-11, Vol. 304, No. 6, This Week's Audio Commentary