I used to think sneezing was just a thing mammals did when dust got up their noses.
Then I spent three weeks on the Galápagos Islands watching marine iguanas—these ridiculous, crusty-looking reptiles that look like miniature Godzillas—and realized that sneezing, at least for them, is less about irritation and more about survival. These creatures dive into the ocean to graze on algae, sometimes holding their breath for up to an hour, and when they surface, they do something that honestly startled me the first time I saw it: they sneeze, violently, spraying a fine white mist into the air. Turns out, that mist is pure salt. Marine iguanas have evolved one of the most elegant solutions to a problem that would kill most terrestrial reptiles—how do you eat in the ocean without poisoning yourself with sodium? The answer, weirdly enough, is to develop specialized nasal glands that concentrate excess salt and then literally blow it out of your face. It’s gross, it’s beautiful, and it’s a reminder that evolution doesn’t care about dignity.
Here’s the thing: when marine iguanas feed underwater, they’re not just nibbling on algae—they’re ingesting massive amounts of seawater in the process. Seawater contains roughly 35 grams of salt per liter, which is way more than any reptile’s kidneys can handle. For most animals, that would be a death sentance. But marine iguanas have a workaround.
The Salt Glands That Changed Everything for These Ocean-Going Lizards
Tucked above each eye, marine iguanas have a pair of nasal salt glands—basically modified tear glands that have evolved to filter sodium chloride out of the bloodstream. These glands are incredibly efficient, concentrating salt at levels that would make a pickle jealous, sometimes up to twice the salinity of seawater itself. The filtered salt collects in a chamber, and when the pressure builds up, the iguana sneezes it out in a jet of briny liquid. I’ve seen them do this dozens of times, and it never stops being weirdly satisfying. The salt dries on their heads, forming crusty white caps that make them look like they’ve been dunked in powdered sugar. Charles Darwin, when he first encountered these animals in 1835, described them as “hideous-looking” and “most disgusting, clumsy lizards,” which—honestly, fair. They do look like something out of a nightmare. But what Darwin didn’t fully appreciate, because the science wasn’t there yet, was just how sophisticated their physiology is.
Wait—maybe I should back up a second. Why are marine iguanas the only lizards on Earth that feed in the ocean? The answer has to do with isolation and necessity. About 5 to 10 million years ago, give or take, land iguanas from mainland South America somehow rafted across hundreds of miles of open ocean to the Galápagos—probably clinging to vegetation after a storm. Once there, they found an archipelago with limited food on land but an abundance of algae in the cold, nutrient-rich waters. Over time, natural selection favored individuals who could tolerate the ocean, dive deeper, hold their breath longer, and most critically, excrete the salt they inevitably swallowed. The nasal glands were key to that transition.
I guess it makes sense that such a bizarre adaptation would evolve in such a bizarre place.
Why Sneezing Salt Is Actually a Brilliant Evolutionary Hack That Saves Energy
The thing that surprised me most when I started reading the research—there’s a great study from the 1980s by physiologist William Dunson—is how energetically cheap this system is compared to kidney filtration. Kidneys work by filtering blood and reabsorbing what the body needs, which requires a lot of metabolic energy. Salt glands, by contrast, are like a one-way valve: they pull sodium and chloride ions directly out of the blood using active transport, powered by sodium-potassium pumps, and dump them into a storage chamber. It’s fast, it’s efficient, and it frees up the kidneys to handle other waste products like urea and uric acid. Marine iguanas basically outsourced their desalination process to a specialized organ, which allowed them to colonize an ecological niche that no other lizard could exploit. And the sneezing part? That’s just the delivery mechanism. Some species of seabirds, like albatrosses and petrels, have similar glands and drip the salt out through tubes in their beaks, but iguanas went for the more dramatic approach.
I’ve watched them sneeze on each other, on tourists, on rocks. It’s constant. And it leaves everything around them encrusted in salt.
There’s also something quietly poignant about the whole thing. Marine iguanas are endemic to the Galápagos, meaning they exist nowhere else on Earth, and they’re vulnerable to climate change, invasive species, and oil spills. Their population crashed during the 1982-83 El Niño event when warming waters killed off the algae they depend on, and some individuals shrunk—yes, shrunk, by up to 20% of their body length—to reduce their energy needs. It’s one of the only documented cases of vertebrate shrinkage in response to starvation. They survived, barely, and when the algae returned, they grew back. But the fact that they can sneeze out salt doesn’t protect them from a warming ocean or a tanker spill. Evolution gave them a superpower, but it’s not a cure-all.
Anyway, I think about that a lot—how adaptation is always situational, always contingent. The marine iguana’s nasal glands are a marvel, but only in the context of the Galápagos. Put them anywhere else, and they’re just another lizard with a weird talent. Which, honestly, is probably true for all of us.
