The 2026 Nobel Prize in Chemistry has been awarded to Henri Kagan of France and Kenso Soai of Japan for discovering how chemical reactions can be made to produce only one of two mirror-image versions of a molecule. The Royal Swedish Academy of Sciences announced the winners in Stockholm. Kagan, born in 1930, is an emeritus professor at the Université Paris-Saclay. Soai, born in 1950 in Hiroshima, is affiliated with the Tokyo University of Science. According to Dutch-language reports, he learned of the prize while shopping and called it one of the happiest days of his life.

The prize concerns chirality, from the Greek word for hand. Many molecules exist in two forms that mirror each other like left and right hands. They have the same composition but can behave very differently. The substance carvone, for example, smells of caraway in one form and of mint in the other, while the two forms of limonene smell of orange and lemon. Our noses detect the difference because the receptors are built from amino acids that are all left-handed. In living organisms, amino acids occur in only one form, and DNA always twists in the same direction. In a laboratory, however, chemical reactions usually produce a roughly equal mixture of both forms.

This matters most in medicine. The Nobel committee noted that a drug may work in one form but be ineffective or even harmful in its mirror image. A well-known example is thalidomide, sold as Softenon in some countries, which in the 1960s was given to pregnant women against morning sickness and caused severe birth defects in thousands of babies. Later research showed that the two forms convert into each other in the body, so making only the 'right' version would not have prevented the disaster. Still, the tragedy underlined why chemists needed ways to make single mirror-image forms.

Kagan took a major step in 1986 with a new way to manipulate reactions using a chiral catalyst, a substance that speeds up a reaction without being used up. He showed that a mixture of left- and right-handed catalysts could enrich one form of the product far more than expected. Soai built on this and, in 1995, found a reaction that yielded just one of the two forms. In 2003 he went further, using an autocatalytic reaction, in which the product itself acts as the catalyst. A tiny initial imbalance becomes self-reinforcing until one form makes up as much as 99.99 per cent of the product. His experiment has been described as one of the most elegant ever performed.

The committee said the work has been revolutionary for chemists developing medicines, flavours, fragrances and new materials, and has helped address a century-old mystery. Soai's result also shows that one form can arise from scratch, though how life on Earth came to favour left-handed amino acids around four billion years ago remains unknown. The two laureates share 12 million Swedish kronor, just over one million euros. The announcement followed the physics prize, with the literature and peace prizes still to come.