There’s a war going on that you’re completely oblivious to, even though it’s happening right under your nose. Well, actually, inside your nose. Rival species of bacteria compete for precious real estate within the damp linings of your nasal passages. In some cases, this microscopic combat works in our favour, when harmless species repress the growth of deadlier ones. But not always – sometimes a species can only gain the advantage over its competitors by becoming more virulent, and we suffer collateral damage.