Tartrazine

Rowlands and Gorecki said that existing methods to turn tissue transparent use solutions that have side effects such as dehydration and swelling and can alter the structure of the tissue. However, tartrazine was used at a low concentration, and its effects were easily undone, potentially facilitating prolonged study of biological processes in live animals, they wrote.

The European Union requires a warning label on products that contain three artificial food dyes approved in the U.S.: Yellow No. 5, also known as tartrazine. Red No. 40, also called E129 or Allura Red AC. Yellow No. 6, called sunset yellow or E110.