This is a video I took of our little one, sitting in a chair watching telly. As I walk over to him the sunlight streaming in through window catches him full in the face, and a couple of seconds later he sneezes.
This happens to him fairly often, usually as we leave the house into the bright sunlight. I noticed this behaviour straightaway, as the exact same thing happens to me when I move from dark to bright light.
It turns out that this doesn’t happen to everyone, as I found out when I said casually to friends, “you know how the sun makes you sneeze, well…”, and was met with stony silence.
Then I found out I had a proper disorder. Gosh!
It’s called a photic sneeze reflex, or as some witty scientists labelled it, Autosomal dominant Compelling Helio-Ophthalmic Outburst – ACHOO syndrome for short. It is estimated that 17-35% of the population have it, and it’s far more common in white people than in other ethnicities.
But no one knows why it happens. Despite it apparently being noticed by Aristotle and investigated by philosopher Francis Bacon, little research has been carried out. My search in the biomedical database PubMed turned up only 16 research papers since 1984.
The best guess at the moment is that it’s because the nerve cells that carry information from the eye and those that carry information from the nose run so close together. As the nerves from the eye are stimulated by bright light, usually to constrict the pupil, electrical signals ‘spillover’ and activate the nerves coming from the nose. This causes the brain to confuse a bright light with a nose irritation, and… ACHOO! In fact, the area of the brain responsible for processing visual information is overstimulated in photic sneezers compared with non-sneezers, which may underlie the spillover effect.
We do know that it appears to run in families – as it has seemingly done in our case – but the genes at the root of it are not known. Initial studies claimed that a child has a 50% chance of inheriting the ‘disorder’ from a photic sneezing parent, but there may be more than one ACHOO gene.
It’s a fairly harmless reaction, though the US air force were sufficiently concerned to fund research into whether this reflex could endanger jet pilots. It could, but was easily overcome with sunglasses.
You may be tempted to speculate as to whether it evolved for a purpose. In all likelihood it didn’t, it is a quirk thrown up by evolution but one that’s not disadvantageous enough to be selected against.
It is irritating, but at least it doesn’t happen during sex.