Common dye turns skin invisible to see the organs inside

A colouring often added to snack foods has the potential to make skin translucent, allowing people to see their internal organs, researchers claim.

Researchers discovered that applying the dye to the skin enabled them to visualise the blood vessels of the brain and observe how the organs and muscles beneath the skin functioned.

The researchers carried out their work on mice. However, they believe the dye is safe for other animals and may be suitable for use on humans as well.

The dye is a type of food colouring, tartrazine, which gives off a yellowish hue. However, this same colour means that it is capable of absorbing light, particularly blue and ultraviolet light.

We usually can't see through skin because it scatters light, just like fog does. However, this product works by altering how skin bends light – essentially making it scatter less and therefore appear more see-through.

Scientists find it easy to apply the dye: they simply rub a solution of the colouring mixed with water into the skin of the animal. A few minutes pass, and the colouring will diffuse, making the skin turn transparent.

Researchers were subsequently able to see the blood vessels and internal organs in the mice, and even observe the muscle contractions that took place as the mice's digestive system operates.

When the experiments are over, the dye can be washed off and the effect will be reversed. Any dye in the skin will simply be absorbed and then passed out in the urine.

The dye itself is considered safe for living things - which is a positive factor, since it's already used in sweets, snack foods and other edible products. It's also been given the go-ahead as safe for use in food by the US Food and Drug Administration.

It remains uncertain whether the method would be successful in humans, whose skin is 10 times thicker than that of a mouse. It may be feasible to utilise a stronger dye or a different delivery method to penetrate all the way through this skin, researchers proposed.

But potentially doing that could enable doctors and healthcare professionals to gain new insights and understanding of what is occurring within their patients' bodies.

“Currently, in human healthcare, we utilise ultrasound to look inside the living body,” Ou said. “Many medical diagnosis platforms are very costly and inaccessible to a wide audience, but systems based on our technology should not be.”

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