The Science of Japan: Hana mizu

If you've spent any time in Japan during the colder months of the year, you will undoubtedly have fallen victim to a phenomenon known to the locals as hana mizu ("nose water"), and to Westerners as a "runny nose." Actually, "watery nose" would be a more apt description, given the consistency of the nasal discharge which tends to be far less viscous than the common garden-variety greenie. As you doubtless will also have discovered if ever you have fallen prey to a bout of hana mizu, the watery drip often makes a stealthy and unwelcome appearance at the most inconvenient of times and locations, being marked neither by the weight or pressure of normal mucus which usually gives the sufferer fair warning.

We in the West have a mortal fear and disgust of bodily fluids. Their proper place, we maintain, is inside the body, and should they make even the briefest of appearances on the outside of the body, such that (gasp!) other people can see them, well that constitutes a social faux pas for which there is almost no recovery. It racks us so with shame and guilt and mortification, that other people should learn that our bodies contain mucus and blood and urine and faeces; we can no longer look our fellows in the eye, but must walk with our heads downcast, disgusting, vile wretches that we are. We can feel the stab of their pointing, accusatory fingers in our backs as we pass: "See that guy? He gets boogers! EWWWWWWWWWWWW"

The Japanese don't seem to have this hang-up quite to the same degree. Just the other day on the train I saw a man in a suit, perhaps on his way to an important meeting or to sell mobile phones, casually brush the tip of his nose, and (picture this in slow-motion if you will, for that's certainly how this shellshocked Western onlooker apprehended it) as his gloved hand pulled away from his face to turn the page of the book he was reading, there appeared a bridge of mizu spanning the chasm between his fingers and his nose, glinting in the morning sunlight. Didn't seem to faze him. But then these people do eat natto.

So, like, what's the deal with hana mizu? Let's start by looking at the malady known as rhinitis, of which there are two kinds. The first is called allergenic rhinitis, and it occurs when an airborne irritant triggers the production of antibodies. These antibodies bind to special cells known as mast cells, which in turn release histamine; and histamine causes inflammation and mucus production in the eyes, nose and sinuses.

The other kind is non-allergenic (or vasomotor) rhinitis. Inside your nose you have blood vessels which contract or dilate in order to control congestion. Sufferers of vasomotor rhinitis have particularly sensitive blood vessels, and certain factors--including changes in weather, certain chemical irritants (e.g. smoke or aerosol sprays), spicy food, and even emotional shocks--can cause overreactions.

(Thankyou, Wikipedia.)

But since not everybody suffers from allergies or hypersensitive nasal blood vessels, why is it that our noses run in cold weather? Julie Mitchell, Associate Professor of Medicine at the Medical College of Wisconsin explains:

While the obvious job of the nose is the sense of smell, the nose's other big job is to ready the inhaled air for the throat, voice box and lungs. The nose warms up and humidifies the air, and it filters out dust, germs, smoke and other particulate matter. Inhaled air picks up heat and moisture as it contacts the inside of the nose, which has grooves and ridges to make a large surface area.

The lining of the nose has glands that secrete water and mucus and, just under the surface, there are hundreds of yards of blood vessels that supply a constant source of heat. (You can see why it's easy to get a bloody nose.)

Under ordinary circumstances, the nose and sinuses produce as much as four cups of mucus every 24 hours. This mucus is constantly being swept back into the throat and subsequently swallowed. On a very cold day, when both the temperature and relative humidity are low, the nasal blood vessels dilate so more blood reaches the nose and thus its mucus and heat machine. Because more liquid is being produced in the nose than can be swept back into the throat, the nose "runs."

On one occasion while I was in Beijing and the outside temperature was in the vicinity of minus 10 degrees Celsius, about a cup of the aforementioned unexpectedly exited my nose as I was stepping down off the tour bus. Luckily nobody saw it happen, and I didn't see where the liquid went, but Emma was reduced to fits of uncontrollable giggling when I told her about it afterwards. A cautionary tale.

(BTW, IANAS, nor am I a doctor.)