For the past 15 years, the favourite theory for the rise in asthma has been the hygiene hypothesis. It runs like this: We wipe surfaces with antibacterial agents, we throw away food that has dropped on the floor and we wash our hands constantly. We have hermetically sealed homes, and our children no longer play outside. They get fewer and fewer infections not only because of their hygienic surroundings but also because they are vaccinated against everything we can find a vaccine for. If a germ gets through all this, we hit it with antibiotics, which clean out the entire gut in one fell swoop. Bacteria and human children no longer co-exist as they did.
