Scientists Discover a Common U.S. Color Additive Turns Mice Skin Transparent

The newest science non-Fiction discovery: optical tissue clearing

Hiya!

In 1898, author H.G. Wells published The Invisible Man, a sci-fi novel about a scientist who finds a way to alter the cells in his body to make himself invisible. The story inspired many film adaptations from as early as 1933 to as recently as 2020, but in 2024, Wells’s concept is stepping off the book pages and television screens and into real life.

While perhaps not quite as dramatic as Wells’s protagonist, scientists have discovered a very real way to turn living tissue into temporary windows revealing muscles, organs, and blood vessels beneath. The technique is referred to as "optical tissue clearing." Even more remarkable than the outcome is the solution they used to achieve it – a common coloring additive found in everything from food to cosmetics in The United States.

The Challenge

H.G. Wells may very well (ha!) have been the first person to popularize the idea of optical tissue clearing, even if it was a fictional concept, but the scientists of the study I’ll tell you about soon weren’t the first to attempt the feat in real life. Experts have been mixing and matching chemicals in an attempt to turn tissue transparent since 1914.

Interestingly, even though The Invisible Man is a science-fiction story, real scientists experimented with the protagonist’s methods — altering the refractive indexes of skin tissue to be more similar. A refractive index measures how a substance, in this case, human tissue, bends light. In other words, how light passes through something.

For instance, skin tissue isn’t typically transparent because light passes through the three main components of skin — lipids, proteins, and water — at different speeds. The point of optical tissue clearing is to make light move at similar speeds as it travels through all the various components of tissue, allowing light to pass through them at the same time.

Scientists have had some success over the years, but despite promising early results, a significant challenge remained.

The problem is that experts have largely been limited to using dead tissue samples for their experiments because the chemicals they’re using, like alcohols and acids, are unsafe for living animals. So, the challenge was for scientists to find a way to achieve optical tissue clearing with living tissue. And guess what? They just did.