Although we generally assume that opacity is the normal look for animals like us humans, this factoid is only correct for as long as you maintain the dissimilar optical refraction indices of skin and the more aqueous underlying structures. What if you could change the refraction index of skin? If you could prevent the normal scattering at the interface, you could reveal the structures underneath, effectively rendering skin transparent. [Zihao Uo] and others demonstrate this in a paper published in Science.
The substance they used was the common food dye known as tartrazine, which also goes by the names of Yellow 5 and E102 when it is used in food (like Doritos), cosmetics, and drugs. By rubbing the tartrazine into the skin of mice, the researchers were able to observe underlying blood vessels and muscles. Simulations predicted that the dye would change the refraction index mismatch between lipids and water which normally causes the light scattering that creates the skin’s opaque appearance. With the dye rubbed into the skin, the effect worked to a depth of about 3 mm, which makes it useful for some research and possible medical applications, but not quite at the ‘jellyfish-transparency’ levels that some seem to have imagined at the news.
Researchers and medical personnel have long wished for this kind of in vivo tissue transparency. A 2019 review article by [Mikhail Inyushin] and colleagues in Molecules provides an overview of the many possible ways, both genetic and chemical, that you might see through skin. Tartrazine has a significant advantage: it is generally considered to be a harmless food dye. In addition, reversing the effect is as simple as washing the dye off.
Naturally, human skin will be trickier than that of mice due to the varying presence of melanin. So it will take more work to use this technique on people, but there are many mice and other common lab test critters who are breathing a deep sigh of relief as the scalpel can be put away for some types of studies.
For now, better to stick with MRI. And fair warning: there’s no need to rush out to rub Doritos on your PCB — it doesn’t work.
Sunburnt intestines! (or at least fat)
The Tartrazine-soaked tissue was only impedance-matched for red light. Other wavelengths still scattered.
Well I can think of one use for this right off, taking blood samples. Anyone who has had a fullbottomist stabbing them like Norman Bates knows exactly what I mean.
I’m sure you mean “phlebotomist“, but “fullbottomist” is hilarious. I’m going to use that one next time I donate blood.
“Fullbottomist” is a “Linda Belcherism” from the animated show Bob’s Burgers.
Never heard of either, but thanks for the detail.
Bob’s Burgers is an absolute treasure of a show.
Bone apple tea problem. English language is full of mixed languages from many Latin based languages like French, Spanish, and German. So trying to know how a word is spelled by pronunciation without knowing the word’s origin have lead to strange spelling.
I once was required to have a series of surgeries requiring inpatient care for weeks. Several times a day, they required blood samples(it was from a major infection). For several days, they would come in and spend up to an hour at a time poke-poke-poking me, even going so far as to utilize a FLIR or ultrasonic imager(which I would love to see covered here) that visualized the structure of the blood vessels under the skin. I have always had notoriously hard-to-stick veins. It was becoming an experience with “enhanced misery”. Sometimes three or four people would take turns trying, gathering around me in wonder at how hard it was to hit a blood vessel – not even taking a break with the stabs. As if it were some kind of competitive sport. It was humiliating and painful.
Then one day I get a very young, 300-pound African-American girl as a blood technician. She comes in and hits the mark on the first attempt. I was pleasantly astonished and so grateful. I christened her the “Vampire Queen” and insisted that she be on my care team. And they accommodated me on that point as much as they could. After that, the stay was much more pleasant. She was a rare master of her craft.
I wonder what’s going on with that mouse abdomen in the “before” shot. Is the mouse under a piece of glass, flattening its belly?
Also this may become the hot party trick of 2025 if it works in humans.
It will be interesting to see what people come up with for Halloween!
It’s not a phase, mom!
I guess it’s a plate of glass (as seen by the outline), ant it was probably spread with some kind of fat to help the skin contact.
The NIH wold seem to disagree here.
The synthetic food dye, Red 40, causes DNA damage, causes colonic inflammation, and impacts the microbiome in mice [ https://www.ncbi.nlm.nih.gov/pmc/articles/PMC10502305/ ]
A Review of the Association of Blue Food Coloring With Attention Deficit Hyperactivity Disorder Symptoms in Children [ https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9573786/ ]
Artificial Food Colors and Attention-Deficit/Hyperactivity Symptoms: Conclusions to Dye for [ https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3441937/ ] (someone had a bit too much fun with this article title!)
In short: We’re starting to find out that food dyes aren’t as harmless as they’re made out to be, though I’d imagine for research purposes, they’re probably… well, to quote Douglas Adams, ‘mostly harmless’.
Any negative effects of food dyes are subtle and only observed over time (the first one subjected the mice to a daily huge dose for ten months); a single acute dose is not associated with any observable negative side effects – or if there are, it’d be less harm than the alternative treatment in a medical context. And the effects are going to be different for consumption vs. topical application.
This is about tartrazine specifically, which does have ongoing research as to actual health effects. So far the research is rather inconclusive, but as a precaution the ingestion of tartrazine is recommended to be limited. Hence the ‘generally considered’ part. You’re right that food dyes like these are best avoided as they serve no purpose other than to make the food or candy look more attractive. But then who wants to eat meat or fish that doesn’t have a fake red colouring and instead looks grey and lifeless? Or candy that doesn’t look vibrant and colourful? Humans can be such picky eaters…
That said, since this particular application does not involve ingestion, it could be considered harmless when rubbed on the skin. Though maybe not every single day, but then that’s true for a lot of substances which we normally consider harmless.
Maya: This is true, but while none of the article titles mention it directly, it does come up in some, if not all, of them.
As far as that goes, it appears that tartrazine is no better than the other food dyes:
— Artificial Food Colors and Attention-Deficit/Hyperactivity Symptoms: Conclusions to Dye for
I’ll also add, anecdotally, that we have a 9 year old with ADHD, and that we’ve observed that his ability to concentrate appeared to improve once we tried cutting artificial food dyes out of his (and by extension, our) diet. I’m not going to claim that his ADHD is ‘cured’ – that would be complete nonsense – but we certainly did perceive a positive behavioral change in him without these dyes. One thing these studies are showing is that these food dyes appear to affect people differently – some have little change with or without it, while others display a fairly vast behavioral change. Additionally, while most of the available research focuses on children, there’s some indication that these effects may extend to adults as well.
That being said, I do agree that for research purposes, like the quite interesting research (transparent skin? woah!) you covered here, it’s likely mostly harmless. I just wanted to point out that perhaps this stuff isn’t as safe as we’ve otherwise come to believe, at least for it’s original intended purpose – and that’s why I chafed at using ‘harmless’ (even in the context of ‘generally considered…’) to describe any of these food dyes, as pedantic as this may appear.
This is true! We’ve come a long way from our hunter/gatherer roots, and these days, we’ve come to expect our food to look, well, appetizing. Some companies are starting to switch to more ‘natural’ coloring as a result of increased public awareness about the potential harms caused by these dyes. Of course, it remains to be seen if any of these newer dyes can be harmful – such is life, unfortunately.
Anyway, I think I’ve derailed the conversation from the transparent skin research long enough, but thank you for responding!
No worries, it’s a good point that deserves some more attention. Here is to a world where these dyes are just used for making lab rats transparent instead of colouring our food for no sensible reason :)
Before you try to be “The Visible Man” model for Halloween, be aware that Tartrazine is a known allergen and there is some evidence of side effects in a relatively small population.
https://en.wikipedia.org/wiki/Tartrazine