Why Reindeer Have Red Noses

Here's something that might just blow your ever-loving mind: Rudolph may not be the only reindeer with a red nose. Thanks to research published today, it appears that reindeer noses are redder than most because they're highly vascularized and chock full of blood.

The paper, published on BMJ.com for the journal's annual Christmas issue, compares the nasal blood vessels of humans (one of which used cocaine for the study, more on that in a bit) and reindeer. Titled "Why Rudolph’s nose is red: observational study," it's the product of a Dutch research team that evidently wanted to see Rudolph's famous red nose could have an evolutionary purpose.

The nose is incredibly important for heating, humidifying, and filtering air, especially in cold climates, but the authors note that little research has been done looking at microcirculation of blood flowing through tiny capillary networks in mammalian noses. As such, the researchers ask if the environment could be behind reindeers' red noses, with more blood flow allowing for better conditioning of air entering through the nose and to help with temperature regulation of the brain.

Which brings us to old Rudolph. The authors hypothesized that Rudolph's red nose may be necessary for dealing with the extreme weather conditions involved with flying across the world in the dead of winter, rather than lighting Santa's sleigh. They write:

Based on the central role of the nasal microcirculation in the temperature regulation of reindeers’ brain and an appreciation of the importance of this for flying reindeer who have to deal with extremes of temperature while pulling a sleigh, we hypothesised that the infamous red nose of the most well known of Santa Claus’s reindeers, Rudolph, would originate from a rich vascular anatomy with a high functional density of microvessels.

To compare nasal blood flow across species, the research team recruited five human test subjects from the Academic Medical Center at the University of Amsterdam, where some of the authors are based, and shoved a video microscope up their noses to chart blood flow. Furthermore, the researchers tested vascular reactivity (i.e. how much the blood vessels can change) by "local application" of 100 mg of cocaine, a common vasoconstrictor used in ear, nose, and throat research, to the interior of one of the subject's noses.

The team then anesthetized a pair of adult reindeer and did a similar microscope survey of blood vessels, then put the reindeer on treadmills to heat them up, and recorded where their heat output was highest with a thermal imager:

The conclusions? Well, aside from the fact that Dutch researchers have cocaine and like to put reindeer on treadmills, the paper shows that reindeer indeed have denser nasal vasculature than humans, which is likely a product of their cold environments. In addition to showing the viability the video microscopes, the team also found glands in nasal mucosa of both humans and reindeer, which they hypothesized may be used for mucous secretion. (The reindeer had higher densities of the gland, which again may have evolved to help humidify dry, cold air.)

That all led to one of the most amusing (and shortest) conclusions I've read in a paper in recent memory:

Using hand-held vital video microscopy for imaging the human nasal microcirculation in health, interventions, and disease, we were able to solve an age old mystery. Rudolph’s nose is red because it is richly supplied with red blood cells, comprises a highly dense microcirculation, and is anatomically and physiologically adapted for reindeer to carry out their flying duties for Santa Claus.

We thank Santa Claus for his enthusiastic support. He was as keen as us to unravel the mystery of his friend’s nose.

Now, I'll be the first to say that this smacks of the type of research that's aimed solely at going viral (hey, it worked!) rather than actually being solid science. And sometimes, when a cleverly- or sensationally-titled press release obfuscates the actual work, it's terrible. But in this case, it's a fairly interesting report, and kudos to the authors for not pretending that their work was more than a fun look at a nagging question. That's respectable in its own right, and it's why most people get into research in the first place. So yeah, sample sizes are really small and it's easy to get cynical about the Rudolph hype, but hey, it's rather cool to see scientists taking their own spin on the holidays.

@derektmead