An international study says mixtures of common chemicals may be teaming up to cause cancer to develop in people's bodies.
The research was carried out by 174 scientists from 28 countries, including Linda Gulliver of the University of Otago.
Dr Gulliver said everyone lived in a chemical soup, with substances in food, air, water and what many people apply to their skin.
She said, when those chemicals worked together, they could become more harmful.
"These chemicals can definitely, once in combination with one another, be able to synergyse to the point where they do definitely enable characteristics to allow normal cells to become cancerous cells."
Dr Gulliver said the research could in the future help to inform agencies such as the Environmental Protection Authority (EPA), which regulated the introduction and use of hazardous substances and new organisms.