Inspired by the research done for the Plastic Soup Foundation, Heidi and Esther decided to study the relationship between the right to regulate and an EU ban on microplastics. In January 2018, the European Commission initiated a restriction procedure on microplastics in cosmetic products. The article deals with the legal implications of a European Union (EU) restriction under the Regulation on the Registration, Evaluation, Authorisation and Restriction of Chemicals (REACH) in relation to the right to regulate in the EU and in the context of the World Trade Organization (WTO). The article argues that in the aftermath of harmonization, the legal scope for EU Member States is dependent on the definition that will be adopted as regards microplastics under REACH: the wider the scope of the restriction, the more probable it is that Member States’ action is restrained. In the context of WTO rules, similar considerations apply as regards the scope of the definition: the wider the scope of an EU ban, the more demanding it will be to satisfy the requirements under the Agreement on Technical Barriers to Trade. Providing scientific evidence is instrumental, as there is little room for the precautionary principle in both regimes.