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Scientists have long debated why whales migrate huge distances from the poles to the tropics—to feed or to give birth? Now, researchers have come up with an alternative theory, published in the journal Marine Mammal Science: Whales move to low latitudes to maintain healthy skin. But vanity would be a crazy reason to travel thousands of miles: Whales have a more important need for keeping their skin in top condition.

As the theory goes, whales foraging in Antarctica’s freezing waters conserve body heat by diverting blood flow away from their skin; this affects skin cell regeneration and suppresses the skin shedding process. By migrating to warmer waters, whales can molt in an environment that requires minimal energy expenditure.

The two lead authors of the study—Robert Pitman and John Durban from NOAA Fisheries Services’ Southwest Fisheries Science Center—first proposed in 2011 that skin molt could drive the migration for certain Antarctic killer whales. With their newly gathered data, they suggest that all Antarctic killer whales—and maybe all whales that migrate to the tropics—are driven by skin molt.

And no, it’s not a vanity thing. Whales in Antarctic waters are often discolored by a thick yellow film of microscopic diatoms. High concentrations of diatoms may also allow potentially harmful bacteria to accumulate. Shed the skin, however, and you jettison the diatoms—along with those pesky bacteria.

Read more here.