Scientists at the University of Texas, Dallas recently discovered that a common food additive can make flesh translucent – literally. Applying a solution of the yellow food colouring tartrazine to the skin of live mice allowed scientists to see right through the skin, into the tissues beneath, potentially offering a simple and inexpensive alternative to conventional imaging technologies like ultrasound.
Through the skin covering the skull, the scientists could look directly at blood vessels on the surface of the murine brain, and through the skin of the abdomen they observed internal organs and even the process known as peristalsis, the contractions that move food through the digestive passage.
Pretty cool, huh?
The physics behind this discovery aren’t actually all that complicated. Basically, when added to water, tartrazine changes the water’s refractive index—the way it bends light—so that it matches the refractive index of molecules like lipids in the skin, reducing the degree to which light scatters as it passes through the skin. Instead of scattering, the light travels straight and true, meaning you get to see what’s on the other side.
The process is totally reversible. It only takes a few minutes, the tartrazine solution can be washed off, and when it is the effects disappear. What tartrazine is absorbed by the skin is metabolized and excreted through the urine.
The researchers’ next goal is to test the solution on humans. Human skin is about 10 times thicker than a mouse’s, so it’s likely a larger dose will be needed, and it’s not clear if the delivery method—just rubbing the stuff on the skin—will be adequate.
A miraculous discovery, for sure, and one that will no doubt benefit medicine. But it’s also a reminder of an unpleasant, dangerous truth about the food supply in America today: that it’s full of substances whose properties and safety we know virtually next to nothing about. There are thousands upon thousands of additives—texturizers, colorings, humectants, anti-fungals, anti-caking agents, preservatives—in Americans’ food that have never been independently tested by the Food and Drug Administration (FDA) or by scientists who aren’t employed by the companies that make those chemicals and add them to their food.