Per- and polyfluoroalkyl substances (PFAS) are synthetic chemical compounds used widely for fundamental everyday products such as textiles, household products, cosmetics, or food processing, thanks to their resistance to heat, water, and oil. However, it has recently been acknowledged that they represent a threat to human health and the environment, given their ability to persist and spread across multiple living organisms (including mammals, plants, and other fauna). They have been linked to different types of health issues, such as tumors and cancers. Given some recent availability of data, this manuscript presents OntoPFAS, the first formal ontology related to PFAS and their relations with the environment and human exposure. The result of this work extensively reuses existing knowledge from different domains, is capable of answering relevant questions, and is compliant with the first PFAS measurements information available. We describe the reasons for this work, its design methodology, the quality of the proposed conceptualization, and the impact in terms of applications for several communities. The resource is available under a free access license: https://github.com/davide1797/PFAS.git .