Researchers have peered into the brains and bodies of living animals after discovering that a common food dye can make skin, muscle and connective tissues temporarily transparent.

Applying the dye to the belly of a mouse made its liver, intestines and bladder clearly visible through the abdominal skin, while smearing it on the rodent’s scalp allowed scientists to see blood vessels in the animal’s brain.

Treated skin regained its normal colour when the dye was washed off, according to researchers at Stanford University, who believe the procedure opens up a host of applications in humans, from locating injuries and finding veins for drawing blood to monitoring digestive disorders and spotting tumours.

“Instead of relying on invasive biopsies, doctors might be able to diagnose deep-seated tumours by simply examining a person’s tissue without the need for invasive surgical removal,” said Dr Guosong Hong, a senior researcher on the project. “This technique could potentially make blood draws less painful by helping phlebotomists easily locate veins under the skin.”