Scent for Change

Without embarrassment and without beating around the bush, Christian Starkenmann reveals an original research project aimed at improving the smell of the toilets of the future.

Combining sensory analysis and molecular biology, he introduces us to the mysteries of olfactory accords, opening the door to a new world in perfumery.

A passionate and inquisitive chemist, this scent hunter has travelled thousands of kilometres, from Geneva to India, via South Africa and Kenya, to put science at the service of the world’s most disadvantaged communities.

He explains the molecular complexity of our most hidden waste, revealing its biological potential and economic value.

With the aim of encouraging the construction and use of toilets for the two billion people who lack access to them, he contributed to the multidisciplinary Reinvent the Toilet Challenge, in collaboration with a private Geneva-based fragrance company and the Bill & Melinda Gates Foundation.

Olfactory Accords for a Better World

This book was born from a scientific collaboration between Firmenich SA and the Bill & Melinda Gates Foundation, at the crossroads of olfaction and sustainable development. It brings together several years of research conducted in sometimes unexpected settings, where smells become vectors of understanding, innovation and even dignity.

The introduction provides a common foundation accessible to all readers. From there, readers are free to choose their own path. Curious scientists interested in neurobiology can dive straight into the chapter devoted to the science of olfaction before moving on to the more surprising chapter on the science of poop. Those who prefer an ecological or humanitarian perspective may begin with the chapter on the world of toilets and then continue in the order proposed. Finally, readers in a hurry, or simply curious, can follow the anecdotes, set in italics, that punctuate each chapter and provide delightful, sometimes humorous interludes.

The book explores a wide range of topics, all connected by a common purpose: understanding how smells, materials and practices can become drivers of transformation. Along the way, readers will discover fMRI experiments showing how the interpretation of the same molecule can vary according to cultural expectations, sanitation facilities assessed for the olfactory quality of their curry, historical distillations of faecal matter, and even experiments using biochar as a fragrance diffuser. The circular economy also has its place, with concrete examples of how excreta can be valorised into animal proteins or innovative materials.

Beyond the diversity of its subjects, this book illustrates the richness of a scientific career driven by curiosity, boldness and commitment. It shows that science can be useful, surprising and deeply human—and that it can inspire many young people to pursue it with passion and freedom.