Blue jeans are a wardrobe staple. But they come at a cost to the environment. To dye denim, manufacturers mix a blue pigment called indigo with harmful chemicals. Waste from this process often pollutes soil and waterways. That led scientists in Denmark to experiment with greener ways to turn jeans blue.

The team turned to indican, a compound that can transform into indigo with the help of an enzyme. An enzyme is a biological molecule that speeds up chemical reactions. The researchers dipped yarn into an indican-enzyme mixture. It turned blue in minutes—without toxic chemicals. The team also dipped yarn in indican and water alone, and discovered something surprising: When exposed to sunlight, it also turned blue! These methods could someday make jeans more eco-friendly.