Rudolph the red-nosed reindeer had a very shiny nose. That part we know, but why did it glow?

Because it’s rich in red blood cells to protect it from freezing and to regulate brain temperature. This superior “nasal microcirculation” is essential for pulling Santa Claus’s sleigh under extreme temperatures, according to a new study in the BMJ.

Researchers in the Netherlands and Norway used a handheld video microscope to assess the noses of five healthy human volunteers and found a circulating blood vessel density of 15 mm/mm2. When the technique was applied to two reindeer noses, the researchers found a 25% higher density of blood vessels, carrying a super-rich concentration of red blood cells.

They also found a high density of mucous glands scattered throughout the reindeer noses, which they say helps “maintain an optimal nasal climate during changing weather conditions and extremes of temperature as well as being responsible for fluid transport and acting as a barrier.” What’s more, infrared thermal images showed that reindeer do indeed have red noses.