Why Do Some People Sneeze When They Go From Indoors Into Sunlight and What Causes a Photic Sneeze Reflex?

Some people sneeze when they go from dark conditions into very bright light because photons get up their nose, or so we’re told.

We think that the answer may be fairly simple: when the sun hits a given area, particularly one shielded or enclosed in glass, there is a marked rise in local temperature.

This results in warming of the air and a subsequent upward movement of the air and, with it, many millions of particles of dust and hair fibers. These particles quite literally get up one’s nose within seconds of being elevated, hence the sneezing.

Many people experience this phenomenon. The behavior is genetic and confers an unrecognized evolutionary advantage.

Sunsneezers seem to be in the minority.

However, as the ozone thins and more ultraviolet light penetrates the Earth’s atmosphere, it will become increasingly dangerous to allow direct sunlight into the eye.

Those of us with the sun-sneeze gene will not be exposed to this, as our eyes automatically close as we sneeze. The rest of the population will gradually go blind, something not usually favored by natural selection.

The tendency to sneeze on exposure to bright light is termed the “photic sneeze”.

It is a genetic character transmitted from one generation to the next and which affects between 18 and 35 per cent of the population.

The sneeze occurs because the protective reflexes of the eyes, in this case on encountering bright light, and nose are closely linked.

Likewise, when we sneeze our eyes close and also water.

The photic sneeze is well known as a hazard to pilots of combat planes, especially when they turn towards the sun or are exposed to flares from anti-aircraft fire at night.

Here are some early thoughts on the subject of light sneezing from Francis Bacon’s Sylva Sylvarum.

“Looking against the Sunne, doth induce Sneezing.

The Cause is, not the Heating of the Nosthrils; For then the Holding up of the Nostrills against the Sunne, though one Winke, would doe it; But the Drawing downe of the Moisture of the Braine.

For it will make the Eyes run with Water; And the Drawing of Moisture to the Eyes, doth draw it to the Nosthrills, by Motion of Consent; And so followeth Sneezing; As contrariwise, the Tickling of the Nosthrills within, doth draw the Moisture to the Nosthrills, and to the Eyes by Consent; For they also will Water.

But yet, it hath been observed, that if one be about to Sneeze, the Rubbing of the Eyes, till they run with Water, will prevent it.

Whereof the Cause is, for that the Humour, which was descending to the Nosthrills, is diverted to the Eyes.”