What causes a sigh?

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Amazingly, if we don’t sigh - we die. And if that’s news to you - well, it was news to scientists. Sadly, they only found out when they first tried making ‘iron lung’ devices to artificially assist breathing, and patients died because the iron lungs didn’t sigh.

It turns out that if you don’t sigh every five minutes, the alveoli start to collapse - and your lungs fail.

They’ve redesigned iron lungs now, of course, and they understand sighing a bit better.

A sigh is a second in-breath. Normally you breathe in, out, in, out. But with a sigh, you take a second in-breath.

Researchers say it is a very basic reflex in humans. In fact, incredibly so: ‘Sighing appears to be regulated by the fewest number of neurons we have seen linked to a fundamental human behaviour’.

Bu although this is how we normally sigh - we sigh like this 12 times an hour - this is not really what we mean when we talk about sighing. Because this sort of sighing happens automatically, and bypasses our consciousness entirely.

We mean an emotional sigh - and researchers do not yet understand this, or have any good explanation. They simply suggest that emotions can trigger this primal sigh reflex: "It may be that neurons in the brain areas that process emotion are triggering the release of the sigh neuropeptides - but we don’t know that."

But this does not really tell us why - and anyway, I am not convinced.

Because it seems clear to me that emotional sighing is a bit like laughter: it seems like a simple physiological reflex, but it’s really a social behaviour.

People don’t tend to laugh alone - they are 30 times more likely to laugh in company (especially mine) - and I think emotional sighing, too, is typically a social act. A communication.

After all, the people who sigh most are young children, and they really exaggerate it - the rising and dropping of the shoulders, the flopping powerless limbs, and so on.

And I think the second most frequent sighers - are parents.

So my theory is: sighing is a performance of exhaustion.

When people lift a heavy weight, for example, they will take a deep breath first to supply themselves with extra oxygen. So I think we perform the act of getting extra oxygen, when facing emotional burdens.

I think that this would also explain why we often roll our eyes to the heaven in mock prayer - which seems unlikely to be a reflex - and sigh the words:

‘Give me strength’.

I suppose it does give us a little strength from the oxygen, but I think it’s probably more about letting others - whether God or parents - know we need it.