Breathe

The first colony on Mars was going so well, up until the day when the first colonist to remove their environmental suit dropped dead.

Tests were run, data collected, theories theorised, and then the next person to remove their suit also died suddenly.

No-one else removed their suits, but they dropped dead soon after.

Robots were dispatched, and everything was fruitlessly analysed, until finally someone had an allergic reaction to a cat back at HQ.

Every human was allergic to Martian dust, and that ended colonisation.

Which makes sense, that's why humanity was sent off Mars in the first place.