The Doritos Ingredient That Turns Mouse Skin Transparent

Who would have thought that a junk food brand featuring products with names like "Doritos Dynamita Sticks: Smoky Chile Queso (Artificially Flavored) Corn Snacks" would come with questionable ingredients? This includes mystery items like Flavor Enhancers 621, 627, and 635 in the Thai Sweet Chili variety. That's in the Australian product line, though. The U.S. Doritos website doesn't disclose ingredients, presumably for what are totally trustworthy reasons. Also, possibly because Doritos make mice's skin transparent and might cause genetic mutations that cause cancer. So there's that.

Okay, at least one Doritos ingredient — yellow 5 — turns mice's skin transparent and might cause genetic mutations that cause cancer. And liver damage, kidney damage, enlarged hearts, missing limbs, or skeletal deformations in unborn babies because it's a neurotoxin, as Very Well Health says. In mice and rats, that is. In humans the Yellow 5 jury is still out, so feel free to chow down at your own risk. So long as you remember that Yellow 5 might potentially contribute to behavioral problems like ADHD. And so long as you remember that humans, rats, and mice are 95% genetically identical. That's why they're good for tests.

But anyway, back to the see-through mice. As The Washington Post explains, it's not as simple as "eat yellow 5, turn transparent as cellophane" or something. In fact, ingesting yellow 5 doesn't turn anything transparent. Rather, the presence of the dye on the skin recrafts light differently, which lets you see what's underneath.

Surely, plenty of folks have gazed upon Doritos and thought, "Hey, these chips are, like, really, really yellow." That would be the yellow 5 — more properly Tartrazine — used everywhere to dye cereal, sauce, yogurt, shampoo, lipstick, vitamins, fabric, and much more, going back to the 1920s. Folks have been raising concerns about the dye's impact on health since then. But if Tartrazine is so ubiquitous and potentially concerning, why is it that we're just learning about its translucent effects right now? 

The answer is simpler than you might think. Researchers at Stanford University set about directly testing Tartrazine because they thought its particles might affect how light refracts. In their study, originally published on the website, Science, they cite the limitations of current imaging technology (think x-rays, MRIs, CT scans, etc.) and ongoing research into more "deep-tissue optical imaging methods" with ultra-techy names like two-photon microscopy, near-infrared-II fluorescence imaging, and optical tissue clearing. 

In short, the experiment worked way better than expected or hoped. As The Washington Post says, researchers physically applied Tartrazine to the surface of mice by massaging onto their skin. After only about five minutes, the mice's skin turned temporarily transparent to the point where the heart, blood vessels, muscle fibers, and more, were clearly visible to the naked eye. No scalpel needed, no invasive procedures, no electronics, nothing. Christopher Rowlands from Imperial College London said that the dye allows for researchers to look 10 times deeper into tissue than otherwise possible.

Some folks might be wondering how in the heck a simple food dye could refract light to the extent that it makes living tissue practically transparent. At least the topical application method answers the question of why nobody has discovered this till now. Nobody's gotten a full-body yellow 5 massage before ... we assume.

But really, there isn't anything at work besides simple optics. Light travels differently depending on the medium, i.e., what it travels through or strikes. Light in space (in a vacuum) strikes less objects than it does on Earth, with its atmosphere of oxygen, nitrogen, argon, carbon dioxide, etc. In general, gas and water make light travel slower and refract more than space. The measurement of how light slows down in a given medium is called the "refraction index." 

A higher refraction index means less scattered light. Certain substances are especially good at raising refraction indices, such as substances with a lot of free electrons. So, just by "slathering mice in a common food dye [Tartrazine]," as Science says, we can create a thin chemical layer over the mouse that raises light's refraction index. Presto: translucent skin. 

Aside from cosmetic procedures like tattoo removal, medical applications include helping to locate tumors and helping to locate blood vessels for withdrawals or injections. And for those concerned about the safety of a yellow 5 rubdown, researchers measured "minimal systemic toxicity" in the mice following the procedure. Just don't try this at home using Doritos.