Joshua Power asked:
My friend has said that if you sneeze with your eyes open, they shoot out! Is this true?
Chris - Well, the answer to this is it is a myth and there's not actually any evidence whatsoever that your eyes are going to leave your head – be reassured.
I know this as well because I've done the experiment on me. I was driving and obviously, it was very unsafe to close your eyes when you feel a sneeze coming on and you're driving because you might leave the road. I forced myself to keep my eyes open but there is a reflex that does close your eyes.
Why should your eyes need to close when you want to sneeze? Well, think about what a sneeze is. When your nasal passages are irritated by something, either something tickling the hairs in your nose, a bug going into your nose, or a virus causing a chemical tickle in your nose, or an allergy then the nervous system is wired up to cause you to release a sudden rush of air straight down your nose. The idea being that this high velocity and in fact, we’ve measured the speed of a sneeze on the Naked Scientists. It’s about 100 miles per hour, it goes at. It’s very fast. Those are the big particles that you can't see.
When the rush of air comes through, obviously, the idea is it’s going to dislodge whatever the irritant is that’s in your nose.
Now, also in your nose are some openings and specifically, there's an opening which is your nasolacrimal duct which carries tears from your eyes down to your nose because you don’t want tears streaming down your face. You want them to go away conveniently into your nose and you sniff them up and swallow them.
If you look in the inner, lower surface of your eyelid, if you follow your lower eyelid ground towards roughly where it meets your nose, you'll see there's a tiny black dot there and that’s called a punctum.
This is like your eye plughole and tears run from the upper outer edge of your eye, across your eyeball, collect in the middle there and go down that hole. It then goes down your nasolacrimal duct and into your nose.
When a sneeze comes along at 100 miles an hour - a big pressure wave - imagine what would happen if that duct stayed patent. All the stuff you're trying to blow out, all of the nasties, all the bogies, and that kind of thing, and the snot, mucus – let’s give it a proper term – would come flying - not just out of your nose - but into your eyes!
This probably wouldn’t be terribly good. It might give you infections. It would certainly jam the duct and that wouldn’t be good.
So, I think the reflexes evolve to make you screw up your eyes. In that way, you compress the duct closed and keep the pressure up in it so that all of the air then rushes out of your nose during the sneeze and stuff doesn’t go up the wrong way.
Georgia - Well, on the subject of hay fever, I was wondering why does it make your eyes itch? I can't fathom the reason for this. I have no self-control. I itch my eyes to death and I feel like I've gone blind. What's going on?
Chris - Well, what is an allergy? When you have an allergy, your immune system has responded to the allergy which is usually a little bit of protein - and pollen has got a lot of protein in it - and that’s why bees go and get it actually because it’s a good source of food for them. The pollen gets on to the antibody called an IgE antibody which is stuck on to cells called mast cells which are in all your tissues.
They're there like depth charges or landmines. They're there as a first defence. The idea being that if something tries to get through your skin or get through your mucus membranes, it triggers these mast cells off so that your immune system gets an early warning that something is trying to come in and it releases all these inflammatory signals saying to the rest of your immune system, “Come in and help me to defend this part of my body.”
But if you’ve got hay fever, instead of having antibodies – these IgE antibodies - there just to detect things like worms, parasites, and other nasties. You’ve got antibodies there that unfortunately get triggered by pollen, which your body should ignore and should regard as innocuous. So, the pollen floats into your eye, lands on these antibodies. They send a signal into the mast cell and it then does what's called degranulate. It discharges this big welt of histamine and other chemicals – they're inflammatory – into the local area where the mast cell is sitting. This goes on to various things including blood vessels and blood vessels in response to histamine open up and this increases the blood flow through the air and making it swell and go red. It also triggers very fine nerve fibres going through the tissue which specifically signal itch and they're activated by histamine. The histamine from mast cell causes the nerve cells to start firing off.
And so, you sense this itchy sensation and you have this desperate urge to rub your eyes. You mustn’t, because the mast cells are also sensitive to being rubbed because if you squish them and squeeze them, it makes them discharge more histamine.
So, if you rub your eyes, you will not only exacerbate the symptom. You will make it much, much worse because you will burst the pollen grains, you will burst the mast cells, and you will make your eye much more sore than if you were just able to resist the temptation and don’t rub it.
So, just to return to Josh’s question, you cannot pop your eyes up by sneezing, because there's no physical connection between your airways and your eyes apart from that nasolacrimal duct, which you probably screw up your eyes to stop yourself filling it with bogies and mucus when you sneeze...