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This is Scientific American’s 60-Second Science. I’m Karen Hopkin, this will just take a minute.

 Anyone who’s ever cut up an onion knows that some smells can actually be painful. Now, researchers from Baltimore and Denver are closer to understanding why. Scientists used to think that odors that are irritating like onions and ammonia directly activate¹ the trigeminal nerve. That nerve responds to touch, temperature and painful stimulation² all over the head. And its fibers³ extend to the membranes⁴ that line the inside of the nose. But the current studies suggest that the trigeminal nerve doesn’t act alone. Specialized⁵ chemosensory cells that line the nasal cavity are actually the first to detect irritating smells. They pass the news to the trigeminal nerve, which then lets your brain know that it’s time to feel the burn and to tear, or cough or gag,or just generally back off. The findings are described in the March issue of the Journal of Neurophysiology.  Having these special sensory⁶ cells as a go-between, the scientists say, might make our nose sensitive to a broader variety of odors, that may not seem like such a bonus. But the system probably evolved to protect us, by giving us a heads-up when we run into something nauseous. It may also keep us from adding too many onions to the spaghetti sauce.

Thanks for the minute. For Scientific American’s 60-Second Science. I’m Karen Hopkin