A major new study has revealed a worrying mix of dangerous chemicals in popular hair extensions, including human hair products. In almost every sample tested, scientists found dozens of substances linked to cancer, hormone disruption, reproductive harm and effects on the immune system. Some products contained flame retardants, organotins and chemicals linked to an increased risk of breast cancer. Certain chemicals in them exceeded European safety thresholds. The study thus confirms the presence of these risky substances in commonly sold products.