Kagan's foundational work showed that a catalyst of imperfect purity could still be manipulated to produce an excess of one mirror-image form of a molecule, yielding a higher-purity product. Soai later discovered conditions under which the catalyst was the molecule itself, letting it replicate through a process called autocatalysis. He showed this process could take a starting imbalance of just 0.00005% between the two mirror-image forms and amplify it into a 99.5% preference for one of them.

Together, the two bodies of work address a longstanding question: why life on Earth is homochiral, building proteins from amino acids that are only in the L-configured form while DNA and RNA sugars are only D-configured.

The stakes of getting mirror-image chemistry wrong were demonstrated by the thalidomide crisis of the 1950s, when a drug sold as a 50:50 mixture of mirror-image forms caused birth defects from one form while the other was safe. Kagan's work is credited with contributing to the development of the anti-HIV drug efavirenz. Soai's research aids the synthesis of drugs including levodopa, used for Parkinson's disease, which must be in its L-form to cross the blood-brain barrier. That synthesis problem was solved in the 1970s by William Knowles at Monsanto using chiral catalysts, work for which Knowles won the Nobel Prize in 2001.

Ibuprofen, developed by Boots in the 1960s, contains an active S-form and an inactive R-form, and the body converts some of the inactive form into the active one. Cells use the D-form of glucose for energy; the mirror-image L-glucose form provides no calories but was judged financially unviable as a commercial sweetener in the 1980s. Chirality also affects the perfume industry, and researchers are exploring applications beyond health, including circularly polarized light displays, anti-counterfeiting security tags and quantum electronics.

Kagan has had a previous brush with the Nobel committee: France's science minister protested his omission from a Nobel Prize in 2001.

The chemistry award follows the 2026 Nobel Prize in Medicine, given on Monday to Karl Deisseroth, Peter Hegemann and Georg Nagel for their work on light-activated ion channels and optogenetics, a technique that allows researchers to control specific neurons using light. Hegemann and Nagel, both German researchers, discovered channelrhodopsin in the early 2000s, a protein from a single-celled alga that acts as a light-activated switch, letting ions into cells to trigger electrical signals when exposed to blue light. Deisseroth introduced the channelrhodopsin gene into nerve cells in 2005, and two years later triggered the light-activated switch in the brains of living mice. Optogenetics has since been used to study the neural circuits behind memory, emotion and psychiatric disease, and is being explored for medical applications including partially restoring vision in blind people.