ROBERT SIEGEL, HOST:

From NPR News, this is ALL THINGS CONSIDERED. I'm Robert Siegel.

And now, some serious science about a silly song.

(SOUNDBITE OF SONG, "RUDOLPH THE RED-NOSED REINDEER")

UNIDENTIFIED MAN: (Singing) Well, you know Dasher and Dancer and Prancer and Vixen.

UNIDENTIFIED GROUP: (Singing) Comet and Cupid and Donner and Blitzen.

UNIDENTIFIED MAN: (Singing) But do you recall the most famous reindeer of all?

SIEGEL: Yes, "Rudolph the Red-Nosed Reindeer." But why is his nose so red? Well, scientists say they have an answer, as we hear from NPR's Sabri Ben-Achour.

SABRI BEN-ACHOUR, BYLINE: Rudolph has long capitalized on his red nose, but sources close to the service animal say he has systematically declined to explain why or how his nose glows so bright, even to Santa. Physiologist Dan Milstein is with the University of Amsterdam. In a recent study, he and a group of colleagues examined the noses of several living reindeer. They propose an answer.

DAN MILSTEIN: There was a much richer amount of blood vessels present inside of the Rudolph's or reindeer's nose in comparison to humans.

BEN-ACHOUR: Rudolph also makes more snot, which may explain his reluctance to go public. All of this blood and snot has to do with the fact that it is freezing cold in the Arctic.

MILSTEIN: It's an adaptation in order to deal with severe weather conditions.

BEN-ACHOUR: Those blood vessels are basically part of Rudolph's internal air conditioner/heater. When Rudolph is resting, all those blood vessels warm the air on the way in. And then as he breathes out, those blood vessels soak up the heat from his breath, keeping him toasty. And when he's overheated, say, from pulling a certain jelly-filled extra jolly payload around, those blood vessels can actually release extra heat. The study appears in the British Medical Journal. For NPR News, I'm Sabri Ben-Achour. Transcript provided by NPR, Copyright NPR.