Is it dangerous to inhale so much of the CO2 we breathe out when we’re indoors? Surprisingly, a new study suggests the answer is yes. Participants in densely populated office environments experienced moderate declines in decision making.

Watch out for combustion byproducts close to your home or office, like tobacco smoke, a leaky furnace or idle car. And if you’re feeling especially cloudy or frustrated, open a window or step outside for a brisk walk. Bonus: it will add to your 10,000-steps-a-day goal for a fitter you!

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